refactor: drop 12 runtimes, keep Claude, Codex, OpenCode, Cursor, ZCode, Antigravity

Removes kilo, kimi, kimi-code, copilot, windsurf, augment, trae, qwen, hermes,
cline, codebuddy and pi end to end: capability descriptors, installer branches
and converters (bin/install.js 14.9k -> 11.2k lines), TypeScript converters,
hook surfaces and runtime homes, review lanes qwen/kimi-code, the two pi
migrations, Kimi payload normalization in the hook guards, dead hostBehaviors
vocabulary, launcher home probes, fixtures, runtime-specific tests and the
prose that presented them as supported.

Installer output for the six kept runtimes is byte-identical to before the
prune. The Kimi tool-vocabulary tests in workflow-guard, read-guard and
read-injection-scanner are left in place pending a decision.

docs/how-to/author-a-host-plugin.md

@@ -21,7 +21,7 @@ from your axes):
 
 | Profile | Example hosts | Binding |
 |---|---|---|
-| `programmatic-cli` | OpenCode, pi | imperative adapter (`createImperativeAdapter`) |
+| `programmatic-cli` | OpenCode | imperative adapter (`createImperativeAdapter`) |
 | `declarative-cli` | Antigravity, Codex | declarative adapter (`createDeclarativeAdapter`) |
 | `ide` | VS Code | imperative adapter + engine-owned hook bus + active model + sandboxed state |
 
@@ -68,7 +68,7 @@ consistency is the contract.
 
 Map the six interface points (command, dispatch, model, hooks, state, artifact)
 to your host's primitives (palette/chat, plugin API, provider calls, etc.). The
-reference host-plugins (OpenCode, Antigravity, pi, VS Code — see Phase 5) are
+reference host-plugins (OpenCode, Antigravity, VS Code — see Phase 5) are
 canonical examples to mirror. Your host-plugin is now a self-contained artifact;
 no msd-core source change is required.