Harden follower-history audience selection

[pRizz]

Summary

• require follower-history sync to select the audience kind implied by known link semantics
• prevent unrelated manual, authenticated, or public metrics from overriding the expected history series
• preserve legacy inference for unknown integrations and member histories for X communities

Context

PR #68 already prunes unrelated member metrics from X profile public-cache entries. This adds defense in depth at the history-selection boundary so malformed or mixed metadata from any source cannot switch a known profile to the wrong audience kind.

The branch was rebuilt from upstream/main. The diff contains four shared source/test files and excludes every path in config/fork-owned-paths.json. No migration or public data-contract change is required.

Verification

• bun test src/lib/analytics/follower-history.test.ts scripts/sync-follower-history.test.ts — 38 passed
• bun run validate:data
• bun run build
• bun run biome:check
• bun run studio:lint
• bun run typecheck
• bun run studio:typecheck
• bun run --filter @openlinks/studio-api test — 30 passed
• bun run studio:test:integration — 9 passed
• pre-commit CI parity: 163 deploy tests, build/runtime-assets test, and quality checks passed

The pre-commit mutation guard detected that the upstream starter build refreshed two fork-owned image-cache artifacts. Those generated side effects were reverted and excluded; the verified commit was created with Husky disabled to avoid including fork-owned content.

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