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.

docs/user/develop/basic/tool.md

@@ -48,5 +48,5 @@ Open `http://127.0.0.1:3080` and ask: `Use the greet tool to greet Ada.` The mod
 ## Next steps
 
 - [Plugin configuration](./config.md) — make the greeting configurable.
-- [Tool authoring reference](../../../cookbook/adding-a-tool.md) — look up nested schemas, canonical values, background work, policy hooks, Code Mode, and UI cards.
+- [Tool authoring reference](../../../cookbook/adding-a-tool.md) — look up nested schemas, canonical values, background work, policy hooks, PTC mode, and UI cards.
 - [Capability layering](../practice/index.md) — split a replaceable capability into Service Definition, Service Provider, and Consumer packages.