feat: add missing integrations and rich notification previews

Add TickTick, Google Calendar, Google Drive and API (WebPage) notification
types, which the backend already supported but the extension ignored.

Fill the previously empty notification previews with content modeled on the
web app: a metadata sidebar (status, priority, assignee, labels, dates,
channel, etc.) plus a markdown body and comment/message threads. Add shared
helpers: PreviewDetail wrapper, TaskMetadata, Slack mrkdwn renderer, GitHub
check/review emoji, and date/HTML utils (cleanHtml strips raw HTML from
GitHub bodies).

The preview metadata "Type" row shows the source item type (Linear Issue,
GitHub Pull Request, Slack Thread, etc.).

Swap list-screen shortcuts: Enter shows details, Cmd+Enter opens in browser.

CHANGELOG.md

@@ -2,6 +2,20 @@
 
 ## [Unreleased]
 
+### Added
+
+- Add support for TickTick, Google Calendar, Google Drive and API (web page) notifications
+- Fill notification previews with rich content (metadata sidebar, body and comment/message threads) modeled on the web app
+- Show the notification source type (e.g. Linear Issue, GitHub Pull Request) in the preview metadata
+
+### Changed
+
+- Swap notification list shortcuts: `Enter` shows details, `Cmd+Enter` opens in browser
+
+### Fixed
+
+- Fix "could not open app" error when opening Google Calendar notifications
+
 ## [0.2.0] - 2024-12-16
 
 ### Added