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

CHANGELOG.md

@@ -6,6 +6,14 @@ All notable changes to Flynn are documented in this file.
 
 ### Added
 
+- **Agent Tool: file.patch** -- Multi-file, multi-hunk structured patch tool. Apply
+  line-based replacements, insertions, and deletions across multiple files in a single
+  tool call. Hunks are applied bottom-up to preserve line numbers. 10 tests.
+- **Gmail Pub/Sub Watcher** -- Automation source monitoring Gmail via Google Cloud
+  Pub/Sub push notifications with polling fallback. OAuth2 auth, configurable watch
+  labels, template rendering with email metadata placeholders (`{{from}}`, `{{subject}}`,
+  `{{snippet}}`, `{{date}}`, `{{id}}`, `{{labels}}`). Wired into daemon lifecycle and
+  gateway (`POST /gmail/push` endpoint). 16 tests.
 - **Inbound Webhooks** -- HTTP endpoints (`POST /webhooks/:name`) that trigger agent
   processing. Config-driven with per-webhook HMAC signature verification, message
   template rendering (`{{body}}`, `{{json.field}}`), and output channel routing.