refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

package.json

@@ -6,7 +6,7 @@
   "type": "module",
   "packageManager": "bun@1.3.11",
   "scripts": {
-    "dev": "bun run --cwd packages/opencode --conditions=browser src/index.ts",
+    "dev": "bun run --cwd packages/tfcode --conditions=browser src/index.ts",
     "dev:desktop": "bun --cwd packages/desktop tauri dev",
     "dev:web": "bun --cwd packages/app dev",
     "dev:console": "ulimit -n 10240 2>/dev/null; bun run --cwd packages/console/app dev",