Add a session Kanban board

[viannaanalyst]

What

Adds a session Kanban board: a new full-screen surface where sessions sit in automatic columns and the only manual transition is archive/unarchive.

• Columns (automatic) — Working (turn in flight) / Needs you (approval or question pending, or a turn that finished while unfocused) / Idle / Archived. Precedence archived → working → needs_you → idle, sorted pinned-first then by recency. Cards carry the reason (Waiting for you / Finished).
• Scope toggle — current project (default) or all projects; all-projects cards show the project name.
• Cards — title, harness icon, repo/branch, relative time, pinned mark, working spinner; click opens the session and closes the board; hover exposes archive/unarchive.
• Drag — drop a card on Archived to archive it, drag it back out to unarchive. 5px threshold, pointer capture only after the threshold (so plain clicks still open), Escape cancels, click suppressed after a drop, data-no-drag targets ignored.
• Entry points — a "Kanban" rail action directly below Inbox and a View menu item on both the in-app menu and the native macOS menu.

No schema or persistence changes: archiving uses the existing session_set_archived path, and the board is derived state (no polling).

Implementation notes

• src/lib/sessionBoard.ts — pure classifier over the canonical merged session list plus the existing live signal sets (busySessionIds, approvalSessionIds, unseenFinishedIds); excludes ephemeral inboxAsk sessions and orchestration workers.
• src/lib/kanbanDrag.ts — pure drop-target helpers (kanbanColumnFromPoint, boardDropOutcome).
• src/surfaces/KanbanView.tsx — the surface (header, scope toggle, columns, cards, drag gesture).
• src/App.tsx — surface lifecycle parity with Inbox/Notes: mutual exclusion, keyboard guards, back navigation, hidden/inert workspace, usage-footer suppression. While the board is open the previously active session counts as unfocused, so a turn that finishes then shows up as "Finished" (and its approval/question banner can fire).
• pt-BR translations for every new string.

Tests

• Web: npm run check:web — 230 files / 2395 tests passed, tsc --noEmit clean.
• Rust: npm run check:rust — fmt clean, clippy -D warnings clean, 310 tests passed.
• New coverage: sessionBoard.test.ts (precedence, needs-you reasons, scope filter, sorting, worker exclusion), kanbanDrag.test.ts (drop matrix, hit test), KanbanView.test.ts (columns, badges, empty hints, all-projects names), ProjectRail.test.ts (rail entry order).

Stacked PR

This branch is based on feat/pr-write-actions (#1). Merge #1 first, or retarget this PR to main after #1 lands.

Pending before merge

• Manual dev-mode walkthrough on real sessions: watch columns move while an agent works and finishes unfocused, click-to-open, drag archive/unarchive with Escape and post-drag click, all-projects toggle, and archived rows persisting across a restart.