agent: dev launcher — own Linux env-var contract, add dev:tauri, doc sweep

The 2026-05-12 engine-slop pass removed runtime std::env::set_var mutation from src-tauri/src/lib.rs and replaced it with warn_if_x11_env_unset_on_wayland. With no launcher owning the contract, Linux Wayland dogfood was about to regress.

run.sh:
- now owns Linux launcher env defaults via case "$(uname -s)"
  LIBCLANG_PATH=/usr/lib64/llvm21/lib64 (user-set wins)
  WEBKIT_DISABLE_DMABUF_RENDERER=1 (always on Linux; user-set wins)
  GDK_BACKEND=x11, WINIT_UNIX_BACKEND=x11 (Wayland only; user-set wins)
- 60s Vite readiness timeout
- detects early Vite exit (kill -0 + wait) instead of hanging forever
- trap installed before wait so Ctrl-C cleans up
- args forwarded: ./run.sh --release etc.
- non-exec final Tauri launch preserved so cleanup trap fires

package.json:
- "dev:tauri": "./run.sh" — canonical discoverable dev command

Docs:
- README, dev-setup, architecture-map runtime + launcher pages updated with the new contract; canonical command is npm run dev:tauri (./run.sh as direct equivalent)
- dev-launcher-and-scripts.md replaces the incorrect "kills process group" claim with honest "kills the spawned npm process"
- dev-setup.md path /CORBEL-Projects/magnotia → /CORBEL-Projects/transcription-app
- gpu-tuning/plan.md gets a superseded note rather than rewriting the original rationale
- engine-slop-residuals.md gains Area F (packaged-binary launcher contract) with honest wrapper-vs-.desktop trade-off documented

Verification: bash -n run.sh; shellcheck clean; cargo check -p magnotia green; npm pkg get 'scripts.dev:tauri' returns "./run.sh"; stale-ref sweep clean across living docs.

package.json

@@ -6,6 +6,7 @@
   "scripts": {
     "dev": "npm run dev:frontend",
     "dev:frontend": "svelte-kit sync && vite dev",
+    "dev:tauri": "./run.sh",
     "build": "vite build",
     "preview": "vite preview",
     "check": "svelte-kit sync && svelte-check --tsconfig ./jsconfig.json",