chore(dev): Add dev runner and split dev ports

Add dev:web (rsbuild) and dev:cli (tttk serve ./content), with dev
running both via scripts/dev.mjs, which shuts both down when either
exits. Also add tttk:inspect for --inspect debugging.

Both servers previously defaulted to port 3000, so the CLI could not
bind while the web dev server was running and the proxy targeted
itself. Pin the web dev server to 5173; the CLI keeps 3000 to match
the proxy. Document the two-process setup and inspector debugging in
docs/development.md.

rsbuild.config.ts

@@ -48,6 +48,9 @@ export default defineConfig({
     },
   },
   server: {
+    // Dev web server runs on its own port; the CLI content server keeps
+    // port 3000 (see the proxy targets below).
+    port: 5173,
     proxy: {
       // Proxy content API requests to the CLI dev server (npm run tttk)
       "/__CONTENT_INDEX.json": "http://localhost:3000",