feat(tui): session filter + reconnect countdown

Tasks 4.2–4.3 of docs/plans/2026-05-17-tui-refactor.md:

- SessionList filters by workflowId (case-insensitive) using
  state.sessions.filter, populated by SubmitInput while in
  InputMode.Filter and cleared on CancelInput.
- TuiWsClient tracks reconnect attempt count and emits
  ConnectionEvent.RetryScheduled(attempt, nextRetryAtMs) before each
  backoff delay. Attempt resets on successful connect.
- StatusBar renders "reconnecting (attempt N, retry in Xs)" with
  recompose-driven countdown.

Also captures a renderer-evaluation note in the progress doc: Mosaic's
ceiling vs Textual, candidate JVM alternatives (tamboui, Kotter,
Lanterna, Mordant), and confirmation that the reducer/Effect core is
renderer-agnostic if a swap is ever pursued.

Pending: 4.1 (scroll log, deferred), 5.1 (coverage gate), 5.2 (cleanup).

docs/plans/2026-05-17-tui-refactor.progress.md

@@ -108,6 +108,22 @@
 [next] 2.3 → 3.1 → 3.2 → 3.3 → {4.1, 4.2, 4.3} → 5.1 → 5.2
 ```
 
+## Renderer evaluation — Mosaic is the floor
+
+Mosaic (jake-wharton/mosaic 0.18) is intentionally minimalist: re-emits plain text lines per frame, no screen-cell buffer, no widget catalog, no built-in borders/modals/scroll regions/mouse, no focus management. We hand-draw `─├┤` in `components/Panel.kt`. That is the entire framing system.
+
+This is fine for a reducer/effect prototype but it caps how polished the TUI can ever look. Compared to Python's Textual we lack: cell-buffer rendering, layout engine, widget library (DataTable / Tree / Input / Modal), focus + mouse, scroll regions, transitions.
+
+**Candidate replacements to evaluate (renderer swap; reducer/Action/Effect core stays):**
+- **tamboui** — user-suggested: https://github.com/tamboui/tamboui (not investigated yet — no web access this session).
+- **Kotter** — Compose-style DSL on JVM, more capable than Mosaic (real text-attribute model, animations, structured input). Closest semantic match to current code.
+- **Lanterna** — Java TUI lib with real `TerminalScreen` buffer, GUI widgets (`Panel`, `Window`, `Table`, `TextBox`), borders, layouts, mouse. Imperative/Swing-style; bigger rewrite of `TuiApp` + `components/` but reducers untouched.
+- **Mordant** — already transitive; only buys nicer ANSI paint, same ceiling as Mosaic.
+
+**Migration cost:** ~all of `apps/tui/src/main/.../TuiApp.kt` and `components/*`. Unchanged: `input/`, `reducer/`, `state/`, `ws/` — the renderer-agnostic core. That's the architectural payoff of Task 2.2/2.3.
+
+**Decision:** deferred. Capture as standalone spec before swapping.
+
 ## Notes for the next session
 - Working tree currently has no commits since `58670a6`; everything is staged-or-modified. Consider committing per task on resume.
 - Kotlin is now 2.2.10 repo-wide; expect occasional `experimental context receivers` warnings (`-Xcontext-receivers`) — future Kotlin will error on this.