chore(tooling): add lint/format gates, pin the toolchain, enforce commit checks

Adds the frontend's first linter and formatter — the Rust half has had
cargo fmt --check and clippy in CI for a while, while 274 TS/Svelte files had
only svelte-check. ESLint runs clean; 159 findings are recorded as warnings
rather than suppressed, so the backlog is visible without painting CI red.

Also: `bun run test` no longer drops into watch mode (the "Before Committing"
list told people to run a command that never returns), the traceability ratchet
moves 82% -> 88%, a pre-commit hook enforces the fast half of that list instead
of relying on memory, the dead webdriverio e2e suite and its five devDeps are
removed, and the Rust toolchain is pinned to 1.97.1 so the developer machine and
the CI builder image stop being five releases apart.

TRACES: | DR-205, DR-206, DR-207

src/lib/services/deviceId.ts

@@ -38,7 +38,7 @@ export async function getDeviceId(): Promise<string> {
     return deviceId;
   } catch (e) {
     log.error("Failed to get device ID from backend:", e);
-    throw new Error("Failed to initialize device ID: " + String(e));
+    throw new Error("Failed to initialize device ID: " + String(e), { cause: e });
   }
 }
 

src/lib/services/playerEvents.ts

@@ -195,7 +195,7 @@ async function handleStateChanged(state: string, _mediaId: string | null): Promi
   switch (state) {
     case "playing":
     case "paused":
-    case "loading":
+    case "loading": {
       // When local playback starts, ensure mode is set to local
       const mode = get(playbackMode);
       if (mode.mode !== "local") {
@@ -236,9 +236,10 @@ async function handleStateChanged(state: string, _mediaId: string | null): Promi
       }
 
       break;
+    }
 
     case "idle":
-    case "stopped":
+    case "stopped": {
       player.setIdle();
       // When local playback stops, revert to idle mode
       const currentMode = get(playbackMode);
@@ -248,6 +249,7 @@ async function handleStateChanged(state: string, _mediaId: string | null): Promi
       }
 
       break;
+    }
   }
 }