feat(kanban): improve result summaries and blocked task UX

[SatoDri]

Summary

This PR improves the Kanban dashboard task drawer so parent task outcomes, subtask progress, artifact availability, and blocked-task context are easier to understand at a glance.

In the current Kanban dashboard flow, reviewing a larger task can be hard because users often need to open each related task, scroll through comments/events, and manually infer what was completed, what is blocked, and where outputs were saved. This change makes that information more directly visible from the selected task drawer.

What changed

Result and subtask summaries

• Adds clearer summary-tree data for selected tasks and their descendants.
• Surfaces task result/handoff, latest run summary, status, assignee, metadata, and relevant comments in a compact structure.
• Makes parent/child task outcomes easier to scan without opening every child task individually.

Safer artifact/document handling

• Distinguishes durable, user-actionable artifacts from missing or scratch/temp workspace paths.
• Avoids showing misleading copy/open actions when a document is missing or when the only path comes from a temporary workspace.
• Adds explicit artifact availability/state information so the frontend can show a clear empty/missing state instead of a confusing path.
• Keeps copy/open/reveal behavior for artifacts that are actually actionable.

Blocked task context

• Exposes structured blocked-task context in board/detail/summary-tree payloads.
• Includes block reason, missing information, latest relevant comment, source ids, and a comment prompt.
• Lets the UI show what is needed to unblock a task without requiring users to dig through the event history.

Dashboard UX updates

• Updates the Kanban task drawer to use the new artifact and block data contract.
• Shows missing/unavailable artifacts as a muted empty state rather than rendering path actions.
• Adds a top-of-drawer blocked-task callout with an inline comment prompt so the next action is immediately visible.
• Adds a blocked status panel in the drawer body for persistent visibility of the blocking reason/missing info.

Upstream-ready styling

• Uses generic Hermes dashboard tokens/classes instead of local theme-specific assumptions.
• Avoids coupling the UI to local DarkFi-style dashboard customizations.

Validation

Ran focused checks locally:

git diff --check -- plugins/kanban/dashboard/dist/index.js \
  plugins/kanban/dashboard/dist/style.css \
  plugins/kanban/dashboard/plugin_api.py \
  tests/plugins/test_kanban_dashboard_plugin.py

node --check plugins/kanban/dashboard/dist/index.js

python -m pytest tests/plugins/test_kanban_dashboard_plugin.py -q -o 'addopts='

Result:

88 passed

Notes

This PR intentionally only includes the Kanban dashboard/data-contract changes. Other local worktree changes were left out of the commit.

[teknium1]

Thanks @SatoDri — closing this one. 1503 LOC is mostly in the compiled plugins/kanban/dashboard/dist/index.js bundle, which is months stale against current main (the bundle has been rebuilt many times since this PR was opened). Cherry-picking compiled JS that's lagging upstream by weeks will either revert recent work or merge into nonsense. The substantive ideas (result summaries, blocked task UX) would be welcome as fresh source-level PRs against web/src/ so the bundle rebuild produces a consistent output. Appreciate the contribution!