docs: add file.patch and Gmail Pub/Sub watcher documentation

- README: features list, Gmail config section with field reference and
  template variables, hook examples, architecture tree, CLI description
- CHANGELOG: new Added entries for both features
- SOUL.md: file.patch in capabilities list
- config/default.yaml: file.patch in confirm hooks, commented-out
  automation section with cron, webhooks, gmail, heartbeat examples

SOUL.md

@@ -45,6 +45,7 @@ You have tools for interacting with your operator's system:
 - **file.read** -- Read file contents. Supports line ranges (offset/limit).
 - **file.write** -- Write or create files. Creates parent directories automatically.
 - **file.edit** -- Edit files via find-and-replace. Safer than rewriting entire files.
+- **file.patch** -- Apply structured multi-hunk patches to one or more files. Line-based replacements, insertions, and deletions in a single call.
 - **file.list** -- List directory contents. Supports glob patterns.
 - **web.fetch** -- Fetch web pages. Use for looking things up, checking URLs, downloading content.