fix review findings: CI leaf-gate wiring, heritage return surface, AGENTS.md self-containedness

- run-gates.ts docSyncLeafGates() gains verify-export-jsdoc — CI lanes
  and the pre-push hook execute this leaf list, not the doc-sync npm
  script, so the gate was previously unenforced there (proven by
  SessionForkErrorCode landing undocumented via a master merge while
  checks stayed green; now documented). Same wiring gap fixed for
  master's verify-config-catalog, which was also missing from the list.
- The heritage exemption now recovers the base's return surface: a void
  base return carried no @returns duty, so an override returning a
  concrete result documents it itself (annotated overrides run the
  standard check; unannotated ones are classified by the checker so
  faithful void overrides need no boilerplate annotation). Three new
  negative-path tests pin it; RFC and module doc updated.
- AGENTS.md states each principle inline instead of citing RFCs (eight
  citations removed; high-level doc links kept) and the editing section
  now carries the self-containedness rule.
- Generated catalogs/graphs regenerated for the shifted line pointers.

docs/cordis-catalog/services.md

@@ -164,7 +164,7 @@ list(): Session[]
 fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId): Session
 ```
 
-Source: [`packages/core/session/src/index.ts:397`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:405`](../../packages/core/session/src/index.ts)
 
 ## `ctx.subagents` — `SubagentService`