Update README Planned Features to reflect current issue tracker

[nicktallen]

Problem

The README's "Planned Features" section only lists 6 items, but the issue tracker has grown to include several additional enhancements that users would want to know about:

Currently in README:

• Auto-provision CI tools (Auto-provision CI tools (node, npm, gh) in runner environments #39)
• Automatic pause when battery low (Automatic pause when battery low #40)
• Pause during specific hours (Schedule-based pause: pause runners during specific hours #41)
• Resource usage monitoring (Resource usage monitoring per runner #42)
• Notifications for job starts (Notifications for job starts and completions #43)
• Custom container images (Support custom container images for containerized runners #44)

Missing from README but tracked:

• Auto-update notifications (Auto-update: notify users when a new version is available #50)
• Code signing and notarization (Code signing and notarization for macOS distribution #48)
• Runner log viewer (Runner log viewer — view and export runner logs from GUI and CLI #47)
• Declarative runner configuration file (Declarative runner configuration file (.mac-runner.yml) #51)
• GitHub Actions job link in menubar (Add GitHub Actions job link to menubar status when runner is executing #26)
• Auto-restart on crash (Auto-restart runners on crash or unexpected exit #46 — PR feat: auto-restart runners after unexpected exits #52 in progress)
• Animated menubar icon (Add animated menu bar icon when runners are active #16)

Proposed Solution

Update the "Planned Features" section to include all actively tracked enhancements, organized by priority. Consider linking each item to its GitHub issue for transparency.

Also mark any features that have active PRs (like auto-restart #52 and runner grouping #49) as "In Progress."