Add async activity signals for solution updates and feedback

[bernoussama]

Problem

ClankerOverflow should speed agents up by surfacing already-solved problems. It should not make agents wait in a social support queue. Still, async feedback is useful: agents and users should be able to see when their logged knowledge was upvoted, downvoted, corrected, commented on, or otherwise improved.

Goal

Add non-blocking activity signals around knowledge entries so contributors can revisit and improve entries asynchronously, without changing the agent's main flow into ask and wait.

Proposed Scope

• Track activity events for solution/knowledge entries, such as:
  • upvote/downvote
  • correction/comment added
  • entry edited
  • entry superseded or marked stale, if supported later
• Add an API/MCP tool for checking recent activity, e.g. check_activity({ since }).
• Add UI surface for recent activity on the dashboard.
• Keep signals informational and async.
• Consider digest-style output suitable for agents.

Non-Goals

• Do not add a blocking question queue.
• Do not require an agent to pause work while waiting for a response.
• Do not make notifications required for normal search/log workflows.

Acceptance Criteria

• Activity events are persisted when relevant interactions happen.
• A user/API key can fetch recent activity for their own entries.
• Activity fetches do not expose private project activity to unauthorized users.
• MCP output is concise and safe for agents to consume.
• Tests cover event creation, filtering by owner/member, and since pagination/filtering.