CP4.3: Language packs: proof.packs, proof.installPack, proof.removePack; Options › Language list, missing-pack bar, About › Language data

- engine `packs`: the packs Backend (the font store on the desktop and CLI, a fixed list in tests
  and ui_shot), the pinned index, installs and removals through craft-font-store's
  `language-pack` kind, craft-proof reading the store's `language-packs/` folder at once.
  Commands open nothing and never turn downloading on (only an Install click in the app does);
  confined automation can't write the packs folder outside its write root.
- ui-egui `language_packs`: File › Options › Language › Language packs (name, size, licence,
  source, Install/Remove, progress, errors), the missing-pack bar (dismissible per document,
  never for a language without a pack), About › Language data (full licence texts).
- CP4.4: `cargo xtask language` (in `ci`): the default build embeds only en-* Language data.
- CP4.5: docs (help, MCP, control protocol, gaps #8, localization parity, roadmap).
- Path deps to Lane 4's worktrees while developing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FypgCX8LsYYE8fsj4byBm2

docs/control-protocol.md

@@ -73,6 +73,11 @@ and set `WORDCRAFT_CONTROL_KEY` to that app's key.
 
 Any other method name is treated as a command id: `{"method": "format.bold"}` works.
 
+Language packs (see [MCP](mcp.md#language-packs)) are commands like any other: `proof.packs`,
+`proof.installPack {"locale": "nl"}` and `proof.removePack {"locale": "nl"}`. Through the control
+channel they act on the running app's packs, and install only while its downloading setting is on;
+they never turn it on. `ui.dialog {"name": "languageData"}` opens About › Language data.
+
 ### Open documents
 
 Several documents can be open at once. Each has an id, a whole number that stays the same while