Add interactive choice-picker menus for finite-choice slash commands

Slash commands with a finite set of options (/reasoning, /fast, ...) now
render a tappable card with buttons (2 per row, ✓ on the current value)
instead of a plain text status card. The mechanism is generic: any command
that calls the adapter's send_choice_picker() gets a picker automatically.

Wire protocol (docs/04, frames.schema.json):
- picker.choice (server→app): {picker_id, title, choices[]}
- picker.select (app→server): {picker_id, value}
- pickers capability flag now True in server_caps

gateway-plugin:
- protocol.py: picker.choice/picker.select frame types + picker_choice()
- dispatch.py: route picker.select → adapter.on_picker_select
- adapter.py: send_choice_picker() (fails cleanly with no live device so
  hermes falls back to text), on_picker_select(), in-memory pending pickers
  (gateway restart expires them; stale select is a no-op), pickers=True

app (KMP):
- Protocol.kt: PickerChoice/PickerChoicePayload + pickerSelectFrame()
- ChatStore.kt: PickerItem + onPickerChoice (idempotent) + resolvePicker
  (optimistic, one-shot)
- ChatDb.kt: persist PickerItem in the messages table (polymorphic decode)
- IrisController.kt: picker.choice routing + selectPicker() action
- ChatScreen.kt: PickerCard composable (locks after selection)

Tests:
- python: 3 picker tests (roundtrip, no-device fallback, stale-select noop)
- kotlin: ChatStorePickerTest (add/idempotent/resolve/one-shot/noop/serialize)
- fixture fix: clear leaked IRIS_HTTP_PORT/IRIS_WS_HOST env so the adapter
  binds the ephemeral port (a prior test's interactive_setup() polluted the
  process env, colliding with a live gateway on 8791)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gateway-plugin/protocol.py

@@ -71,6 +71,10 @@ TYPE_SEARCH_RESULTS = "search.results"
 # Slash-command catalog (app's "/" drawer)
 TYPE_COMMANDS_CATALOG = "commands.catalog"
 
+# Interactive pickers (slash-command choice menus, e.g. /reasoning, /fast)
+TYPE_PICKER_CHOICE = "picker.choice"
+TYPE_PICKER_SELECT = "picker.select"
+
 # Reconnect catch-up (M3 outbox; extended by M5 push)
 TYPE_SYNC = "sync"
 TYPE_SYNC_DONE = "sync.done"
@@ -606,6 +610,37 @@ def commands_catalog(commands: list[dict[str, Any]], *, id: int | None = None) -
     )
 
 
+# ---------------------------------------------------------------------------
+# Picker frames (interactive slash-command choice menus)
+# ---------------------------------------------------------------------------
+
+
+def picker_choice(
+    picker_id: str,
+    title: str,
+    choices: list[dict[str, Any]],
+    chat_id: str,
+    *,
+    thread_id: str | None = None,
+) -> Frame:
+    """Event: an interactive choice picker (one tap → one value).
+
+    Used by slash commands with a finite option set (``/reasoning``,
+    ``/fast``, …) on platforms that support pickers. The app renders the
+    title + choice buttons and answers with a ``picker.select`` frame
+    carrying the same ``picker_id``. Outboxed, so a reconnecting device
+    re-renders a still-pending picker.
+
+    Each choice: ``{"value": str, "label": str, "is_current": bool}``.
+    """
+    return Frame(
+        type=TYPE_PICKER_CHOICE,
+        chat_id=chat_id,
+        thread_id=thread_id,
+        payload={"picker_id": picker_id, "title": title, "choices": choices},
+    )
+
+
 # ---------------------------------------------------------------------------
 # Sync frames (M3 outbox)
 # ---------------------------------------------------------------------------