fix(examples): drop mastra's typecheck:channel — it can never pass

channel-host.mts imports src/agent.ts, which transitively pulls in
src/mastra/** — and that tree has a pre-existing "Type 'Memory' is not
assignable to type 'MastraMemory'" error unrelated to the Channel host.
TypeScript follows imports regardless of tsconfig `include`, so no
scoping fix exists; a typecheck script that can never pass just trains
people to ignore it.

Removes typecheck:channel from mastra/package.json only — the channel
script and tsconfig.channel.json (still used for module resolution) are
unchanged — and leaves a comment in tsconfig.channel.json explaining why
this starter alone has no such script. Every other starter keeps
typecheck:channel.

examples/integrations/mastra/package.json

@@ -9,8 +9,7 @@
     "dev:debug": "LOG_LEVEL=debug npm run dev",
     "build": "next build",
     "start": "next start",
-    "channel": "tsx --tsconfig tsconfig.channel.json channel-host.mts",
-    "typecheck:channel": "tsc -p tsconfig.channel.json --noEmit"
+    "channel": "tsx --tsconfig tsconfig.channel.json channel-host.mts"
   },
   "dependencies": {
     "@ag-ui/client": "0.0.57",

examples/integrations/mastra/tsconfig.channel.json

@@ -1,4 +1,13 @@
 {
+  // Unlike every other starter, this config has no matching `typecheck:channel`
+  // script in package.json. `channel-host.mts` imports `src/agent.ts`, which
+  // transitively pulls in `src/mastra/**` — and that tree has a pre-existing
+  // `Type 'Memory' is not assignable to type 'MastraMemory'` error
+  // (src/mastra/agents/index.ts:18) unrelated to the Channel host. TypeScript
+  // follows imports regardless of `include`, so `tsc -p tsconfig.channel.json
+  // --noEmit` can never pass here and there is no scoping fix. This config is
+  // still used by the `channel` script (via `tsx --tsconfig`), which only
+  // needs it for module resolution, not a clean typecheck.
   "compilerOptions": {
     "target": "es2022",
     "module": "esnext",