Split adapter.py monolith into focused modules; restore Ruff complexity defaults (issue #12)

adapter.py was a 3,493-line monolith. Split it into focused modules with
clear separation of responsibilities, bringing it down to ~857 lines:

- Module-level helpers: hooks, classify, pickers, commands, setup,
  defaults, secrets
- Frame-handler mixins: inbound, tool_frames, push_frames, media_frames,
  picker_frames, channel_frames, query_frames
- mixin_base: IrisAdapterBase (declaration-only base for shared attrs)
- adapter.py now holds only IrisAdapter (the composition of the 7 mixins
  + BasePlatformAdapter), register(), and test-facing re-exports

The mixins come before BasePlatformAdapter in the MRO so their methods
override the base; super() calls (e.g. send_image) still resolve to
BasePlatformAdapter. No circular imports; dispatch.py and http_server.py
(instance-method callers) are unaffected.

Ruff complexity ceilings (PLR0911/0912/0913/0915) restored to Ruff's
built-in defaults (12/50/6/5) instead of "just above the current maxima",
which ratchets the bar down as code grows. The existing genuinely-complex
functions (frame builders mirroring the wire schema, the QR matrix builder,
the dispatch table) carry an explicit `# noqa: PLR09xx` marking them as
reviewed, frozen exceptions; new code is held to the default ceilings.

All 125 tests green (94 test_android + 31 test_android_http); no new ruff
errors introduced.

gateway-plugin/protocol.py

@@ -388,7 +388,7 @@ def message_update(
     )
 
 
-def message_stop(
+def message_stop(  # noqa: PLR0913
     chat_id: str,
     message_id: str,
     final_text: str,
@@ -428,7 +428,7 @@ def message_stop(
 # ---------------------------------------------------------------------------
 
 
-def tool_start(
+def tool_start(  # noqa: PLR0913
     chat_id: str,
     index: int,
     name: str,
@@ -472,7 +472,7 @@ def tool_progress(
     )
 
 
-def tool_end(
+def tool_end(  # noqa: PLR0913
     chat_id: str,
     index: int,
     name: str,
@@ -694,7 +694,7 @@ def sync_done(cursor: int, *, id: int | None = None) -> Frame:
 # ---------------------------------------------------------------------------
 
 
-def history(
+def history(  # noqa: PLR0913
     chat_id: str,
     messages: list[dict[str, Any]],
     has_more: bool,
@@ -755,7 +755,7 @@ def message_deleted(
 # ---------------------------------------------------------------------------
 
 
-def notification(
+def notification(  # noqa: PLR0913
     chat_id: str,
     kind: str,
     title: str,
@@ -807,7 +807,7 @@ def status(state: str) -> Frame:
 # ---------------------------------------------------------------------------
 
 
-def media_offer(
+def media_offer(  # noqa: PLR0913
     media_id: str,
     kind: str,
     mime: str,