Fix registry URL and add registry browser to TUI

- Fix default registry URL: gitea.brrd.tech -> cmdforge.brrd.tech
  (gitea.brrd.tech was Gitea's API, not CmdForge registry)

- Add "Registry" button to TUI main menu
- Add registry browser overlay with:
  - Search input with live search
  - Tool list with owner/name display
  - Info panel showing name, publisher, version, description,
    downloads, and tags
  - Install button with confirmation dialog
  - Proper error handling for network issues

Co-Authored-By: Claude Opus 4.5 <[email protected]>

src/cmdforge/config.py

@@ -16,7 +16,7 @@ CONFIG_DIR = Path.home() / ".cmdforge"
 CONFIG_FILE = CONFIG_DIR / "config.yaml"
 
 # Default registry URL (canonical base path)
-DEFAULT_REGISTRY_URL = "https://gitea.brrd.tech/api/v1"
+DEFAULT_REGISTRY_URL = "https://cmdforge.brrd.tech/api/v1"
 
 
 @dataclass