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/secrets.py

@@ -0,0 +1,29 @@
+"""Scope-aware secret reads for the iris plugin.
+
+Shared by ``adapter.py`` (token / TLS / FCM credentials) and ``setup.py``
+(config probes + env enablement).
+"""
+
+import os
+
+from agent.secret_scope import UnscopedSecretError as _UnscopedSecretError
+from agent.secret_scope import get_secret as _scoped_get_secret
+
+
+def _get_scoped_secret(name, default=None):
+    """Scope-aware credential read with the default-profile startup fallback.
+
+    Secondary profiles construct their adapters under a profile secret scope
+    -- the scope is authoritative and a scoped miss returns ``default`` (no
+    cross-profile borrow from ``os.environ``, which may hold another
+    profile's value). The DEFAULT profile's adapter constructs and sends
+    *unscoped* under multiplexing, where a bare ``get_secret`` would raise
+    ``UnscopedSecretError`` and crash this path; there ``os.environ`` is that
+    profile's own value, so fall back to it. Same pattern as the IRC
+    ``IRC_SERVER_PASSWORD`` read (``plugins/platforms/irc/adapter.py``).
+    """
+    try:
+        val = _scoped_get_secret(name, default)
+    except _UnscopedSecretError:
+        val = os.getenv(name)
+    return val if val is not None else default