feat: add TUI card detail pane

[aksOps]

What changed

• add a read-only card detail overlay opened with Enter or a board-card click
• render description and comment Markdown through Glamour after reducing it to the frozen web allowlist
• show checklist state, labels and link:: chips, blocker edges, comments with author/date, and killed-card context
• reconcile open details after external board changes, coalescing enrichment reloads and closing deleted task snapshots
• bound scrolling across input, resize, and content changes; cache rendered body lines outside scroll and view hot paths
• preserve frozen JavaScript Markdown semantics for source ordinals, ASCII word boundaries, whitespace, and line separators
• keep detail state and rendering in internal/tui/carddetail, with only input, refresh, and view delegation in the root model

Impact

Board users can inspect the complete persisted card without leaving the TUI. Open details follow server-authoritative edits, unsupported Markdown remains literal, source list ordinals are preserved, enrichment failures stay scoped, and stored terminal content cannot widen the pane.

Validation

• go test ./internal/tui/... -count=1 (80 passed)
• go test ./internal/tui/... -count=10 (800 passed)
• GOFLAGS=-buildvcs=false go test -race ./... -count=1
• GOFLAGS=-buildvcs=false sh scripts/check-go-coverage.sh (96.7% total; 95.4% internal/tui; 96.9% internal/tui/carddetail)
• sh scripts/check-go-format.sh
• sh scripts/check-go-checkers.test.sh
• GOFLAGS=-buildvcs=false go vet ./...
• GOFLAGS=-buildvcs=false go build ./...
• go mod verify
• git diff --check origin/main..HEAD

Closes #86

[sonarqubecloud]

Quality Gate passed

Issues
9 New issues
0 Accepted issues

Measures
0 Security Hotspots
97.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud