agent: lumotia — pin rust toolchain + workspace clippy/fmt sweep

rust-toolchain.toml pins to stable 1.94.1 so contributors and CI runners
share the exact rustc / rustfmt / clippy versions. Without the pin, every
machine surfaces a different lint set depending on its local install — six
pre-existing lints showed up on 1.94.1 that 1.93-era HANDOVER reported clean.

Clippy fixes (all pre-existing, not introduced by feature work):

- crates/storage/src/database.rs: std::iter::repeat().take() -> repeat_n()
- crates/llm/src/lib.rs (docs): "+ frontends" was parsed as a markdown bullet
  continuation by rustdoc, breaking doc-lazy-continuation. Reworded to "and".
- crates/llm/src/lib.rs (loop): while-let-on-iterator -> for-loop.
- src-tauri/src/commands/security.rs: .iter().any(|a| *a == x) -> .contains(&x).
- src-tauri/src/lib.rs: io::Error::new(Other, e) -> io::Error::other(e).
- src-tauri/src/tauri_app_data_migration.rs: drop function-tail `return`s
  inside cfg blocks; each platform's block now ends with a tail expression.

cargo fmt sweep across the workspace. Mechanical layout-only changes;
no semantics affected.

Workspace gates after this commit:
- cargo fmt --check: clean
- cargo clippy --workspace --all-targets -- -D warnings: clean
- cargo test --workspace: 405/0 (will become 409/0 with Phase A.1+A.2)

src-tauri/src/commands/live.rs

@@ -427,9 +427,7 @@ impl LiveSessionRuntime {
         // the dimensions are real. Validation-window drops can fire
         // before any chunk reaches `process_audio_chunk`; they get
         // attributed at the next reconciliation once we know the rate.
-        if self.state.last_chunk_sample_rate == 0
-            || self.state.last_chunk_samples_per_chan == 0
-        {
+        if self.state.last_chunk_sample_rate == 0 || self.state.last_chunk_samples_per_chan == 0 {
             // Roll back the consumed delta so we re-observe it once
             // we have dimensions to convert it with.
             self.state.last_dropped_chunks = self.state.last_dropped_chunks.saturating_sub(delta);
@@ -1111,11 +1109,8 @@ fn maybe_dispatch_chunk(
     let parent_span = tracing::Span::current();
     thread::spawn(move || {
         let _parent = parent_span.enter();
-        let inference_span = tracing::info_span!(
-            "inference",
-            chunk_id = current_chunk_id,
-            duration_secs,
-        );
+        let inference_span =
+            tracing::info_span!("inference", chunk_id = current_chunk_id, duration_secs,);
         let _enter = inference_span.enter();
         let audio = AudioSamples::mono_16khz(chunk_samples);
         let started = Instant::now();