feat(notifications): config-as-code recap channel/cadence overrides in .gittensory.yml focus manifest

[JSONbored]

Config-as-code parity for the recap knobs: let the .gittensory.yml focus manifest override the recap enable/cadence/channel settings so operators configure the digest as code, not only via env. Follow the existing manifest field-plumbing in src/signals/focus-manifest.ts (resolveEffectiveSettings, read by src/settings/repository-settings.ts:40) — the same layering used for other per-repo review knobs.

Deliverables

• Add recap fields (enabled / cadence / channel) to the focus-manifest schema + resolveEffectiveSettings in src/signals/focus-manifest.ts, resolved by src/settings/repository-settings.ts:34
• Env stays the fallback; manifest > env precedence documented and enforced (yml > DB > defaults per the config-as-code convention)
• Unit test: manifest override wins, env fallback applies when absent, invalid manifest value falls back (all branches)

References

• src/signals/focus-manifest.ts
• src/settings/repository-settings.ts:34
• src/settings/gittensory-repo-focus-manifest.ts

Part of #1963.

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size: S · held for later release (gittensor:feature once activated)

[linear-code]

JSO-2351