rename code-mode to ptc (PTC mode), except session-persistent vocabulary

Rename the tool-presentation transport from code-mode to ptc everywhere
that is not written into session logs: the mode config value becomes 'ptc',
the preset directory/id becomes ptc, the demo becomes demo:ptc, the
dispatch waterfall becomes tools/ptc-dispatch-log (types PtcDispatch*), the
prompt rule becomes tools:ptc-only, source/test files become ptc.ts etc.,
and prose says PTC mode / PTC 模式. The session-persistent vocabulary
(durable events tool/code-dispatch*, logged plugin name tools-code-mode,
sub-call id segment :code:) intentionally stays and moves in the stacked
persistence PR, which is blocked until the SESSION_FORMAT_VERSION v0→v1
migration lands with it. run_code, its code parameter, CodeSdkLanguage,
CodeRunFailedError, the dsh-code-runtime family, third-party codex names,
and frozen archived notes keep their names.

AGENTS.md

@@ -80,7 +80,7 @@ pnpm run doc-sync       # all documentation gates; leaf list in scripts/run-gate
 pnpm run test:docs      # quick documentation checks (no build; doc-quick aggregate)
 pnpm run website:build  # VitePress build (doubles as dead-link check)
 pnpm dsh --profile headless "task"  # run one task from source (needs DEEPSEEK_API_KEY)
-pnpm run demo:code-mode -- "task"  # headless Code Mode run (needs key)
+pnpm run demo:ptc -- "task"  # headless PTC mode run (needs key)
 ```
 
 ### Host sandbox failures