feat(maestro-tui): SessionTask + SessionEmulators + ResizeTracker (NAP-279)

Per-attached-session task:
- Owns one WS to `WS /api/attach/:id` and a `vt100::Parser`.
- Binary frames → `parser.process(bytes)`. Text frames → `ClientControl::Ping`
  is replied to as Pong; other text frames are ignored in v1.
- `SessionInput::Bytes(b)` becomes a binary frame; `Resize { cols, rows }`
  resizes the parser AND sends `ClientControl::Resize` on the wire.
- WS drop → `Reconnecting` with exponential backoff (1s → 30s, ±25% jitter).
  Parser screen is **not** reset across reconnects, so the user keeps seeing
  the last-known frame instead of a blank.
- `SessionHandle::end()` transitions the task to `Ended` and stops it.

SessionEmulators:
- `(SessionId → SessionHandle)` registry.
- Owns a `ResizeTracker` whose `set_pane_size(sid, pane_id, (cols, rows))`
  and `session_size(sid) -> Option<(cols, rows)>` compute the per-dimension
  minimum across all panes bound to the same session — the value the
  dispatcher feeds to the daemon.

Tests:
- 7 unit tests for `ResizeTracker` covering per-dim min, cross-session
  isolation, and pane/session drop semantics.
- 2 unit tests for `SessionState` transitions.
- 1 axum-WS round-trip integration test asserting `"hello"` lands in the
  vt100 screen within 500ms.

Cargo.toml

@@ -38,6 +38,7 @@ toml = "0.8"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 uuid = { version = "1", features = ["v4", "serde"] }
+vt100 = "0.15"
 
 [profile.release]
 lto = "thin"