activity: integrate with frontend

[arthyn]

This fixes LAND-1516. In integrating with the frontend I found quite a few things that needed to change with our types. The main backend changes that happened were:

• Fully fleshed out the source type and use that instead of the previous mix of source and *-concern types.
• Made sure each source includes enough information to find the parent source so that we can do defaulting correctly
• Add notified to events so we can track whether something was notified historically (which may be different from our current settings)
• Changed volume settings to use a map instead of signifiers so that levels can be adjusted granularly. Allows us to move to a new default while migrating old users with the current default
• Made unread-summary more generic so that it can be used nested/recursively
• Cleaned up some of the more confusing type names

Frontend-wise:

• Added new activity firehose subscription to track all activity events
• Adjusted all unreads usage to use new activity agent data
• Disconnected thread unreads from main window
• Adjusted default unread color to be gray-400 and only show blue when there are unread/unseen notifications
• Changed UnreadIndicator so it can be passed whether an unread has notifications
• Adjusted volume setting to work with new map system

To do in another PR:

• Allow notification settings for threads
• Remove current "full-info" scry on frontend and wrap unreads into a new init scry
• Add reaction events and any other event types we could conceive of
• Integrate with activity feed
• Show unread counts based on a setting?
• Verify everything is in mark-warmer that needs to be

PR Checklist

• Includes changes to desk files
• Describes how you tested the PR locally (test ship vs livenet)
• If a new feature, includes automated tests
• Comments added anywhere logic may be confusing without context

Targets #3354.

[arthyn]

This is just for unread flow. Going to follow-up with notification volume/mutes, and updating unread flow to make threads and main window separate.

[linear]

LAND-1516 activity: integrate new agent with frontend

[patosullivan]

Code looks mostly good, just some nits on imports, errant console logs, etc.

[Fang-]

As discussed:

[Fang-]

This addressed all my feedback. Should be Fine Now™.