[codex] Add federation export preflight scaffold

[mashbean]

Summary

• Adds server-side federation export eligibility scaffolding for selected public Matters articles.
• Adds author/article federation setting migration scaffold for durable export policy state.
• Adds optional strict gate support in FederationExportService by joining user_federation_setting and article_federation_setting only when requested.
• Adds decisionReport support with selected, eligible, skipped, and per-article gate reasons.
• Preserves coverage from each Jest shard by writing shard coverage into separate coverage/* subdirectories before Codecov upload.
• Updates @matters/ipns-site-generator to published 0.1.9 for existing server IPFS publication compatibility, but removes the Fediverse bundle generation path from matters-server.

Architecture boundary

• matters-server owns DB state, public-only rules, opt-in gate decisions, and read-only candidate loading.
• matters-server no longer builds ActivityPub bundles, writes export files, or exposes a federation export CLI.
• Bundle generation and retryable publication are being moved to lambda-handlers in https://github.com/thematters/lambda-handlers/pull/217.

Safety

• No production credentials are used.
• No production migration has been run.
• No production deployment is included.
• No ActivityPub delivery, IPFS/IPNS publishing, background job, or file writing is attached to the server runtime.

Validation

• Node 18 npm run build passed locally.
• Targeted federation export service Jest passed locally: 9/9.
• federationExportService.ts targeted line coverage is 100% locally.
• Targeted ESLint passed locally.
• git diff --check passed locally.
• Repository pre-commit hook build/gen/lint/format completed.

Current gate

• PR remains draft for engineering review and develop/staging validation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.56%. Comparing base (a0b044b) to head (cfd0cb6).

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #4761       +/-   ##
============================================
+ Coverage    57.82%   71.56%   +13.74%     
============================================
  Files         1008     1011        +3     
  Lines        19868    20031      +163     
  Branches      4259     4308       +49     
============================================
+ Hits         11489    14336     +2847     
+ Misses        7649     5230     -2419     
+ Partials       730      465      -265     

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[zeckli]

Leave one comment, but it's not a blocker.

[zeckli]

I think we don't support article id anymore 🤔