TUI comments and link management (parity+)

[aksOps]

Question

The capabilities the server always had and the web UI never used: add comments from the card view (delete where sensible), and manage blocks/blocked-by links between cards (create, remove, display both directions, blocked-gate visibility). This is deliberate parity-plus per the map decisions. Resolution: merged PR.

Part of #80.

Blocked by: #90

[aksOps]

Resolved by PR #107, squash-merged as 2bc82d023106944632eb1e65a6213b0a774592d7.

Acceptance verified: direct-store comment add/confirmed deletion, directional blocker-link add/unlink, both-direction rendering, explicit completion-gate state, nested input ownership, session-safe async reconciliation, canonical post-write refresh, and transactional Done-drop guarding. Exact-head Regression, Sonar, CodeQL, and Socket checks passed.