Add Gitea integration for agent to push branches and open pull requests

- Implemented `register-gitea-bot.sh` to provision Gitea access token.
- Updated `maintainer.py` to support Gitea API for push and PR operations.
- Modified `install.sh` to warn if Gitea token is not provisioned.
- Enhanced documentation in `README.md`, `CLAUDE.md`, and `architecture.md` to reflect new Gitea functionality.
- Added Gitea configuration to `config.example.json`.

config.example.json

@@ -20,6 +20,16 @@
 
   "state_file": "/home/paul/.local/state/semprini-maintainer/state.json",
 
+  "gitea": {
+    "api_base": "https://git.semprini.me/api/v1",
+    "web_base": "https://git.semprini.me",
+    "user": "claude-code",
+    "repo": "paul/semprini-core",
+    "token": "FILLED_BY_register-gitea-bot.sh",
+    "git_author_name": "Claude Code",
+    "git_author_email": "claude-code@semprini.me"
+  },
+
   "matrix": {
     "homeserver": "https://matrix.semprini.me",
     "user_id": "@maintainer-bot:semprini.me",