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/qr.py

@@ -232,7 +232,7 @@ def _version_info(version: int) -> int:
     return _bch(version, 12, 0x1F25)
 
 
-def _build_matrix(version: int, level: str, codewords: list[int], mask: int) -> list[list[bool]]:
+def _build_matrix(version: int, level: str, codewords: list[int], mask: int) -> list[list[bool]]:  # noqa: PLR0912,PLR0915
     size = 17 + 4 * version
     # matrix[r][c] = dark; reserved[r][c] = function module (not data)
     matrix = [[False] * size for _ in range(size)]
@@ -355,7 +355,7 @@ def _build_matrix(version: int, level: str, codewords: list[int], mask: int) ->
     return matrix
 
 
-def _mask_bit(mask: int, r: int, c: int) -> bool:
+def _mask_bit(mask: int, r: int, c: int) -> bool:  # noqa: PLR0911
     if mask == 0:
         return (r + c) % 2 == 0
     if mask == 1: