feat(core): add authoritative agents.manifest.json + optional contract description

OTAIP had four overlapping notions of "which agents exist" (discovery,
count-agents, docs/agents.md, the contract registry). This adds one
generated source of truth.

- scripts/generate-manifest.ts (`pnpm gen:manifest`) writes committed
  agents.manifest.json: every discovered agent with has_contract
  first-class, plus action_type + input/output JSON Schema (via the same
  zodToJsonSchema the tool catalog uses) for the 18 contracted agents.
  `--check` mode fails if the committed file is stale; wired into CI.
- Add optional `description` to AgentContract; the catalog/describe_agent
  generator uses it (falling back to the previous string). Authors fill it
  as agents graduate — no bulk, domain-inventing schema generation.

This is the OTAIP-honest answer to "one schema for every agent": the
two-tier model is made queryable rather than papered over.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 2 people

.github/workflows/ci.yml

@@ -46,6 +46,12 @@ jobs:
       - name: Verify built bundles load
         run: pnpm verify:dist
 
+      # The committed agent manifest must match what the generator produces
+      # from discovery + contracts. Fails loud if a contributor changed an
+      # agent or contract without regenerating `agents.manifest.json`.
+      - name: Verify agent manifest is up to date
+        run: pnpm gen:manifest --check
+
       - name: Type check
         run: pnpm run typecheck