fix(markets): stabilize sector valuation coverage

[koala73]

Summary

Fixes #5903.

• Add a bounded authenticated Yahoo v7 batch fallback for symbols omitted by individual responses. The local authenticated batch probe returned all 12 sector valuations, including XLK, XLV, XLY, and SMH.
• Persist complete core valuation snapshots even when v7 return metrics are null, and reuse missing symbols only as explicit stale last-good records.
• Publish current valuation count and stale-symbol provenance separately; MCP filtering preserves partial status and current counts.
• Keep direct/proxy/field-level diagnostics and truthful SECTOR_VALUATIONS_PARTIAL semantics when stale data is used.

Verification

• Focused Yahoo/sector/MCP tests: 85 passed.
• Health classification/verdict/history tests: 123 passed.
• npm run typecheck: passed.
• npm run typecheck:api: passed.
• npm run test:data: passed.
• Pre-push gates: passed.

Production was still reporting 8/12 before this branch was deployed. After merge/deploy, verify two consecutive five-minute production cycles at 12/12 with sourceStatus: ok before closing the issue.

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Project	Deployment	Actions	Updated (UTC)
worldmonitor	Ready	Preview	Aug 4, 2026 8:35pm