refactor(v3): reorganize styles per client library - #455

* feat(djangocms-blog): pagination

* feat(pagination): WIP See `TODO` and `XXX`

- 🚧 bootstrap4 .pagination
    - ✅ default
    - 🐞 tacc (CMS/Portal)
        - UI bugs
        - consider combining
- ✅ djangocms-blog .pagination
- ❌ TACC .c-page
    - deleted out of ignorance
    - must be restored
    - reference provided

* fix(pagination): skin (color, border, outline, …)

- 💡 bootstrap4 .pagination
    - ✅ default
    - ✅ tacc (CMS/Portal)
        - 💡 consider combining
- ✅ djangocms-blog .pagination
- ❌ TACC .c-page
    - deleted out of ignorance
    - must be restored
    - reference provided

* refactor(pagination): link vs link--end

* docs(pagination): TODO @import x-link x-button

* refactor(pagination): __item & __link → vs __…-item & __…-link

* fix(pagination): skipped bootstrap link blue

* chore(pagination): re-order style and remove cruft

* fix(pagination): button (as link) looses width

* refactor(pagination): assume links are <a>

* enhance(pagination): edge cases

* fix(pagination): cms & portal match but are split

* fix(pagination): easy button links & square links

* fix(c-page): restore

* fix(c-page): restore it as it was, no c-pagination

* feat(pagination): tools/x-pagination demo

* fix(pagination): consistent border-radius

- components/c-page
- bootstrap4/pagination
- tools/x-pagination

* fix(pagination): consistent skip/etc links

* refactor(pag…): disabled/active links → modifiers

* enhance(pagination): disabled link for c-page

* fix(pag…): c-page should NOT use button class

* fix(pag…): list too tall, inconsistentent w/ x-…

* enhancepagination): consistent demos

* chore(pagination): mark all demos as ready

* fix(pagination): bootstrap discrepancy

* feat!: bootstrap4 WIP

* fix(v3): nav bootstrap css load bugs

* refactor(v3): Nav: Nav Tabs → Nav: Tabs

* feat(v3): bs4 grid reorg

* conf(v3): move subdir definition to subdir

* feat(v3): distinguish global styles demo/set…/base

* fix(v3): lost col demo styles

* docs(v3): grid belongs in layout

* fix(v3): grid css moved so update core-styles

* docs(v3): move bs4 nav to bs4 components

* docs(v3): figure belongs in content

* docs(v3): order bs4 categogories

* refactor(v3): move remaining bs4 patterns

* docs(v3): match bootstrap 4 pattern naming

* enhance(v3): hack to support tacc btns in modals

* docs(v3): extra note about TACC modal button hack

* refactor(v3): move all bs4 .postcss into child dir

* fix(v3): user expects nav-tabs.css not tabs.css

## Overview

Import path fix since latest merge of `epic/v3`.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Wesley B <wesleyboar@users.noreply.github.com>

epic/v3's content (incl. main, via #680/#682) was already applied to
epic/v3--reorg via #681's chain propagation, but #681 was squash-merged,
severing the ancestry link again (same issue as #680 on epic/v3).
Recording this merge with the 'ours' strategy (verified zero net
content change) so future `git merge epic/v3` (and transitively
`git merge main`) operations compute the correct merge-base.

Resolves PR #455 conflicts caused by main's PR #683 (x-lead/s-lead
extraction, headings-as-v2/v3 bridges) landing at pre-reorg paths.

- placed new tools/trumps/elements files under their tacc/ subdir,
  per this branch's client-library reorg
- updated their @import/link paths for the new directory depth
- kept the reorg's `shouldLoadBootstrap4` context key, added the new
  `cms-v3` headings variant using it

Second pass at resolving #455: epic/v3 gained one more merge from
main since #701 (39d9944), re-opening the conflict. This time it
merged clean — no manual resolution needed.

# Conflicts:
#	src/lib/_imports/bootstrap4/components/nav/tabs/tabs.postcss
#	src/lib/_imports/core-styles.cms.v3-bridge-for-v2-users.postcss
#	src/lib/_imports/tacc/elements/headings-as-v3.postcss
#	src/lib/_imports/tacc/elements/headings/config.yml

…#703)

## Overview

Hardcodes `heading-N--v2`'s values instead of proxying the live
`heading-N` mixins.

## Related

- #693

## Changes

- **changed** `heading-2`/`heading-3`/`heading-4` in
`x-headings--cms.postcss` to hold v3's redesigned values directly
- **hardcoded** `heading-N--v2` in `x-headings.cms.v2.postcss` with v2's
original per-level values

## Testing

1. `npm install`
2. `npm run build:css`
3. `npm start`
4. Open `/components/detail/headings--cms`
5. Compare against its pre-PR state (no visual change expected)
6. Open `/components/detail/headings--cms-v2`
7. Compare against its pre-PR state (no visual change expected — that's
the whole point of hardcoding)

## Overview

Fixes a compound-vs-descendant selector bug that silently dropped the
heading reset (and now the margin baseline) on every native h1-h6 in
main content.

## Changes

- **fixed** `&:is(h1,h2,...)` to `& :is(h1,h2,...)` in the three
`:--main-content`-scoped heading files — the missing space compounded
onto the container selector instead of selecting its descendants, so it
never matched a real heading
- **added** a Bootstrap-mimicking margin baseline to the shared
`heading` mixin, so h4-h6 (previously undesigned) get the same treatment
h3 already had
- **dropped** the now-redundant Bootstrap4 load from the plain
CMS/CMS(v2) demo variants and the `docs-vs-bootstrap` variant, now that
#702 unified TACC's and Bootstrap's `.h1`-`.h6`

## Testing

1. `npm install`
2. `npm run build:css`
3. `npm start`
4. Open `/components/detail/headings--cms`
5. Native h1-h6 now get the line-height reset and margin baseline that
never applied before this fix

## Overview

Splits TACC's `.h1`-`.h6` classes into their own file so Bootstrap's
typography-headings module reuses it instead of redefining it.

## Related

- #689

## Changes

- **added** `heading-classes--cms`/`--docs` (`.h1`-`.h6` classes, per
theme) and `heading-N--cms`/`--docs` mixins
- **updated**:
    - native `h1`-`h6` elements files
    - Bootstrap's typography-headings module
    - CMS/Docs bundles that use them

## Testing

1. `npm install`
2. `npm run build:css`
3. `npm start`
4. Open https://localhost:3000/components/detail/headings--cms
5. Compare against its pre-PR state (no visual change expected)
6. Open https://localhost:3000/components/detail/headings--docs
9. Compare against its pre-PR state (no visual change expected)

## Notes

Bootstrap's typography-headings module isn't imported by any production
bundle today — because Core-Styles base is required even for Bootstrap
skin — but kept it in sync for demo.

## Overview

Deletes the bare heading-N mixins now that nothing but their own
--cms/--docs wrappers referenced them.

## Related

- #702

## Changes

- **deleted** the bare `heading-N` mixins, moving their declarations
directly into `heading-N--cms`/`heading-N--docs`

## Testing

1. `npm install`
2. `npm run build:css`
3. Confirmed `core-styles.cms.css` and `core-styles.docs.css` compile
byte-for-byte identical to before

# Conflicts:
#	src/lib/_imports/components/tacc-docs.postcss
#	src/lib/_imports/elements/headings--docs.postcss
#	src/lib/_imports/tacc/tools/x-headings--cms.postcss
#	src/lib/_imports/tools/x-headings.postcss

…ly files

wy-breadcrumbs.postcss and x-headings.cms.v2.postcss don't exist on
main/epic/v3, so the mixin-prefix-rename merged in from main didn't
touch their `@mixin x-breadcrumbs*`/`@mixin x-lead` calls.

# Conflicts:
#	src/lib/_imports/tacc/components/c-button/c-button.postcss
#	src/lib/_imports/tacc/tools/x-button.postcss
#	src/lib/_imports/tacc/tools/x-button/_x-button--tag.hbs
#	src/lib/_imports/tacc/tools/x-button/config.yml
#	src/lib/_imports/tacc/tools/x-button/demo.css
#	src/lib/_imports/tacc/tools/x-button/x-button.hbs