M0: toolchain, monorepo scaffold, gateway plugin skeleton, CMP app

- gateway-plugin/: android platform plugin (plugin.yaml + adapter.py
  register(ctx) + no-op AndroidAdapter) + stub modules for M1-M5
- app/: Compose Multiplatform project (shared KMP + androidApp +
  desktopApp) with Gradle wrapper; builds :androidApp:assembleDebug
  and :desktopApp:compileKotlin
- scripts/guard_hermes_agent.sh + pre-commit hook: fail if hermes-agent/
  is staged (read-only reference, never committed)
- .gitignore excludes hermes-agent/; docs/ reference library

gateway-plugin/protocol.py

@@ -0,0 +1,22 @@
+"""Frame schemas -- the single source of truth for the wire protocol.
+
+Every frame the plugin sends/receives is modelled here as a dataclass +
+constants. ``docs/protocol/frames.schema.json`` is generated/mirrored from
+this module, and the Kotlin side mirrors these shapes (see
+``docs/04-wire-protocol.md``).
+
+Milestone M1: hello/hello.ack, message, error, ping/pong.
+Milestone M2: message.start/update/stop, reasoning, tool.*, commentary, typing.
+Milestone M3: channel.*, search, sync.
+Milestone M4: media.*.
+Milestone M5: notification, fcm.register, read.receipt.
+"""
+
+PROTOCOL_VERSION = 1
+
+# Frame type constants (the ``type`` field of every frame).
+TYPE_HELLO = "hello"
+TYPE_HELLO_ACK = "hello.ack"
+TYPE_ERROR = "error"
+TYPE_PING = "ping"
+TYPE_PONG = "pong"