ci: enforce clippy -D warnings and cargo audit as hard gates

Flip both CI gates from informational to hard-fail (SPEC-001 quality gates):
- clippy: `-- -D warnings` on the server crate. Cleared the debt via clippy --fix
  (unused imports/style), targeted #[allow(dead_code)] on native-remote-control
  future API, and #[allow(clippy::too_many_arguments)] on 3 protocol-mirroring fns.
- cargo audit: hard-fail with documented per-ID --ignore flags (rsa RUSTSEC-2023-0071
  unfixable/unreachable in active tree; gtk-rs + glib Linux-only tray backend not
  compiled into the Windows agent; proc-macro-error build-time). New advisories fail.
- Move [profile.release] to the workspace root (it was silently ignored in the server
  member), activating lto/codegen-units/strip.

No behavioral changes. Reviewed and gates verified passing on the build host.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/api/downloads.rs

@@ -7,13 +7,13 @@
 
 use axum::{
     body::Body,
-    extract::{Path, Query, State},
+    extract::Query,
     http::{header, StatusCode},
     response::{IntoResponse, Response},
 };
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
-use tracing::{error, info, warn};
+use tracing::{error, info};
 
 /// Magic marker for embedded configuration (must match agent)
 const MAGIC_MARKER: &[u8] = b"GURUCONFIG";