chore(api): sync barrel exports across api package

[yassinedorbozgithub]

Summary

Syncs the barrel files across packages/api/src so that every module's public
symbols are actually re-exported from the package root. Adds two missing barrels
(health/index.ts, mcp/index.ts) and wires them into src/index.ts, plus ~90
previously unexported symbols across audit, extensions, workflow,
transfer, utils, helper, user, i18n, websocket, bindings, and
database. Export-only change — no runtime logic was touched.

Why

@hexabot-ai/api ships a single root entrypoint (exports: { "." : ... }), so
the barrel files are the public API surface for extension authors. Modules
added over recent PRs (MCP tokens, health service, sqlite-vector/pgvector RAG
stores, audit exporters and interceptors, workflow contexts/seeds/schemas,
transfer adapters) landed without their barrel entries, leaving them
unreachable to consumers of the published package.

How to review

• packages/api/src/index.ts — the two new
  top-level re-exports (./health, ./mcp); confirm both belong in the public
  surface.
• packages/api/src/mcp/index.ts and
  packages/api/src/health/index.ts — new
  files; check that nothing internal-only is being leaked (guards, repositories,
  entities are exported deliberately, matching how other modules do it).
• packages/api/src/extensions/index.ts
  and packages/api/src/workflow/index.ts —
  the two largest additions; worth a check for naming collisions between
  export * sources, since duplicate symbol names across barrels surface as
  ambiguous exports rather than hard errors.
• The remaining files are one-to-four-line additions and can be skimmed.

Validation

• pnpm --filter @hexabot-ai/api build — TypeScript compiles and dist/index.d.ts
  resolves all new re-exports.
• pnpm --filter @hexabot-ai/api lint
• pnpm --filter @hexabot-ai/api test
• No behavioral change expected: diff is additive export * from lines only
  (git show --stat → 15 files, 178 insertions, 0 deletions).