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)

crates/transcription/src/local_engine.rs

@@ -199,8 +199,7 @@ impl LocalEngine {
         let backend = guard.as_mut().ok_or(Error::EngineNotLoaded)?;
 
         let start = Instant::now();
-        let segments =
-            backend.transcribe_sync_with_abort(audio.samples(), options, abort_flag)?;
+        let segments = backend.transcribe_sync_with_abort(audio.samples(), options, abort_flag)?;
         let inference_ms = start.elapsed().as_millis() as u64;
 
         Ok(TimedTranscript {
@@ -272,7 +271,9 @@ pub fn load_whisper(model_path: &Path) -> Result<Box<dyn Transcriber + Send>> {
 mod tests {
     use super::*;
     use std::sync::atomic::Ordering;
-    use transcribe_rs::{ModelCapabilities, TranscribeError, TranscribeOptions, TranscriptionResult};
+    use transcribe_rs::{
+        ModelCapabilities, TranscribeError, TranscribeOptions, TranscriptionResult,
+    };
 
     #[test]
     fn engine_reports_not_available_before_loading() {