Release metadata refresh: bump to v0.6.5 and capture post-v0.6.4 shipped changes

[Copilot]

The repo was still labeled at v0.6.4 despite multiple merged changes since that release point. This PR updates release metadata so the current state of master is represented consistently.

• Release version alignment

  • Bumped app version from 0.6.4 → 0.6.5 in:
    • root package.json
    • apps/backend/package.json
    • apps/frontend/package.json

• Changelog catch-up

  • Added a ## [0.6.5] - 2026-04-19 section in CHANGELOG.md.
  • Documented key shipped work since v0.6.4, including:
    • bulk issue status updates (desktop multi-select actions)
    • workflow optimization to skip docker build/publish on agent-only changes
    • AI analysis server-mapping fix
    • backend lint blocker cleanup

// package.json (root/backend/frontend)
{
  "version": "0.6.5"
}