build: doc-sync gates — typecheck doc code blocks + verify event taxonomy (RFC 006 pts 1-2)

Two tsx CI gates make doc/code drift fail fast:
- doc-typecheck extracts every fenced ts block from README/docs/package READMEs,
  compiles them with tsc --noEmit against a temp project (vendor->lib, harness->src
  paths from tsconfig.typecheck.json), and fails on errors. Deliberate sketches opt
  out with ```ts ignore-check; the opt-out ratio is reported and capped.
- verify-event-taxonomy asserts the docs/architecture.md taxonomy table names
  exactly the events declared in the interface Events blocks. This surfaced three
  events the table had been missing (tools/change, llm/adapter-change,
  system-prompt/change), now added.

Doc snippets made compilable with stub imports/declares (1 genuine sketch ignored).
Wired into CI after typecheck. API reports (RFC 006 pt 3) deferred. Graduates RFC
006 pts 1-2 -> ADR 0014.

packages/invariants/README.md

@@ -9,8 +9,11 @@ Dev-mode event-contract invariants and session-log freeze. A pure-listener plugi
 A functional plugin — register the module namespace (this is what loading by name in `cordis.yml` does):
 
 ```ts
+import type { Context } from 'cordis'
 import * as Invariants from '@deepseek-ai/dsh-invariants'
 
+declare const ctx: Context
+
 await ctx.plugin(Invariants)                     // freeze on (default)
 await ctx.plugin(Invariants, { freeze: false })  // assert contract, don't freeze
 ```