Clear cargo warnings: drop v2.1 classifier scaffold, annotate tool_router

Three of the four dead-code warnings (`ClassifierHint`, `PolicyClassifier`,
`NoopClassifier`) were the v2.1 classifier scaffold sitting unused since
PR-1. Deleted — being unused for weeks was a stronger "no concrete plan"
signal than its presence was a "TODO" signal. Trivial to re-add when we
actually do the classifier (v0.4.0 candidate).

Fourth warning was rmcp's `#[tool_router]` macro generating internal
references to a `tool_router` field on TileService that rustc's dead-code
pass can't see through. Added `#[allow(dead_code)]` with a brief comment
on why.

`cargo build` is now clean of the four standing dead-code warnings.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src-tauri/src/mcp.rs

@@ -301,6 +301,10 @@ pub struct TileService {
     pending: Arc<PendingActions>,
     rate_limiter: Arc<WriteRateLimiter>,
     app: AppHandle,
+    // Used by the code rmcp's `#[tool_router]` macro generates; rustc's
+    // dead-code pass can't see through the macro, hence the explicit
+    // suppression rather than a redesign.
+    #[allow(dead_code)]
     tool_router: ToolRouter<Self>,
 }