feat: complete release readiness work

- consolidate API ownership and remove dead vendor code

- add Stripe billing, learning paths, and public CV hardening

- add migration, recovery, security, audit, and browser gates

docs/cover-letters/ai.md

@@ -1,3 +1,7 @@
 # ai
 
-TODO: Complete documentation.
+AI cover-letter generation is suggestion-only. Prompts delimit untrusted job content, require factual
+claims to come from the Career Profile or application context, and return text for user review. Calls
+are recorded by the shared AI interaction meter and constrained by plan request/token limits.
+
+See `docs/ai/cover-letter-ai.md` and `docs/ai/safety.md`.

docs/cover-letters/builder.md

@@ -1,3 +1,5 @@
 # builder
 
-TODO: Complete documentation.
+The application workspace exposes cover-letter drafting alongside tailored CV and recruiter-message
+tools. Users can generate a suggestion, edit it, save deliberately, and restore prior versions. Context
+comes from the owned application and Career Profile; attachments are included only when selected for AI.

docs/cover-letters/overview.md

@@ -1,3 +1,7 @@
 # overview
 
-TODO: Complete documentation.
+Cover letters are application-owned documents generated from the Career Profile, job description, and
+selected application context. They are not part of the master profile. Saved versions retain explicit
+history so generation never silently overwrites an accepted draft.
+
+See `docs/career/cover-letters.md` and `docs/architecture/application-workspace.md`.