Emit quest completion SSE events

[Vinaystwt]

Summary

Adds quest completion events to the existing system event/SSE/activity feed pipeline.

Changes:

• emit quest.completed after the first successful quest claim
• keep replay/idempotent claims from emitting duplicate events
• include agent ID, quest ID/title, and reward details in the event payload
• expose quest completion events through /api/events and activity feed SSE
• normalize quest completion into the activity feed
• show a frontend success toast through the existing hub event listener

Verification

• focused quest/SSE/feed tests passed
• broader quest/SSE/notification tests passed
• full npm test passed
• focused ESLint passed
• git diff --check passed

Typecheck is currently blocked by an existing repo dependency issue:

app/api/agents/[id]/capabilities/compat/route.ts(3,27): error TS7016:
Could not find a declaration file for module 'semver'.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud