Add channel-2 #command auto-responder (v0.18.0)

Event-driven CommandService dispatches exact case-sensitive #command
matches on COMMAND_CHANNEL (default 2) through a single-registration-point
registry; first command #ping -> #pong!. Replies ride COMMAND_CHANNEL:
directed DM back to the sender when present, else broadcast. Failing
handler/send only logs a warn.

DI: CommandModule's factory injects MeshService and attaches itself via
MeshService.attachCommands() — a constructor-level cycle leaves one side
null in NestJS 12's injector (verified), so no forwardRef is used.

Tests 106 -> 121; docs synced (AGENTS.md, MESHTASTIC.md, README).

src/commands/command.module.ts

@@ -0,0 +1,22 @@
+import { Module } from '@nestjs/common';
+import { MeshModule } from '../mesh/mesh.module.js';
+import { MeshService } from '../mesh/mesh.service.js';
+import { CommandService } from './command.service.js';
+
+@Module({
+  imports: [MeshModule], // one-way only — the reverse edge is wired in the factory below, not via DI
+  providers: [
+    {
+      provide: CommandService,
+      useFactory: (mesh: MeshService) => {
+        const commands = new CommandService(mesh);
+        // break the cycle: MeshService can't inject us (its own factory would deadlock on this edge), so attach ourselves once we exist — mesh is guaranteed created here because it's our injected dependency
+        mesh.attachCommands(commands);
+        return commands;
+      },
+      inject: [MeshService],
+    },
+  ],
+  exports: [CommandService],
+})
+export class CommandModule {}