feat(selfhost): config-lint helper that surfaces .gittensory.yml parse warnings with friendly messages

[JSONbored]

parseFocusManifestContent (src/signals/focus-manifest.ts:1043) silently degrades a broken config to an empty manifest with a warnings[] array — an operator whose private per-repo config (src/selfhost/private-config.ts) has a YAML typo gets deterministic-only reviews and never knows why. Add a pure lintManifestText(text): {ok, warnings[], summary} helper that runs the existing parser and formats its warnings into an operator-facing report (valid-YAML-but-no-fields, oversize, malformed, unknown top-level keys). No new parser — reuse the existing one.

Deliverables

• Add lintManifestText in a new src/selfhost/config-lint.ts that calls parseFocusManifestContent and returns {ok:boolean, warnings:string[], recognizedFields:string[]}
• Detect and warn on unknown top-level keys by diffing parsed object keys against the recognized set
• ok=true only when warnings is empty AND at least one recognized focus field was parsed
• Do NOT emit or echo any values from the config (paths/labels are policy) — report field NAMES only
• Unit tests: valid config (ok), malformed YAML, oversize, empty-but-valid, unknown-key warning — cover both arms of the ok condition

References

• src/signals/focus-manifest.ts:1043
• src/signals/focus-manifest.ts:1015
• src/selfhost/private-config.ts:69

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size: M · gittensor:feature

[linear-code]

JSO-2196