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/audio/src/streaming_resample.rs

@@ -77,9 +77,7 @@ impl StreamingResampler {
             INPUT_CHUNK,
             1, // mono
         )
-        .map_err(|e| {
-            Error::AudioDecodeFailed(format!("StreamingResampler init failed: {e}"))
-        })?;
+        .map_err(|e| Error::AudioDecodeFailed(format!("StreamingResampler init failed: {e}")))?;
 
         Ok(Self::Sinc {
             resampler,
@@ -110,9 +108,7 @@ impl StreamingResampler {
                     let chunk: Vec<f32> = residual.drain(..INPUT_CHUNK).collect();
                     let input = vec![chunk];
                     let result = resampler.process(&input, None).map_err(|e| {
-                        Error::AudioDecodeFailed(format!(
-                            "StreamingResampler process failed: {e}"
-                        ))
+                        Error::AudioDecodeFailed(format!("StreamingResampler process failed: {e}"))
                     })?;
                     if let Some(channel) = result.into_iter().next() {
                         out.extend_from_slice(&channel);
@@ -144,9 +140,7 @@ impl StreamingResampler {
 
                 let input = vec![chunk];
                 let result = resampler.process(&input, None).map_err(|e| {
-                    Error::AudioDecodeFailed(format!(
-                        "StreamingResampler flush failed: {e}"
-                    ))
+                    Error::AudioDecodeFailed(format!("StreamingResampler flush failed: {e}"))
                 })?;
 
                 let Some(mut out) = result.into_iter().next() else {