chore(lint): pin Rust toolchain to 1.95 and adopt clippy 1.95 suggestions

- Add rust-toolchain.toml to align local and CI Rust versions, eliminating
  clippy roulette caused by `dtolnay/rust-toolchain@stable` drift.
- Fix 9 clippy 1.95 findings introduced by Hermes Phase 4-8 modules:
  * 4x unnecessary_sort_by  -> sort_by_key (with Reverse for desc)
  * 3x collapsible_match    -> match guards
  * 1x while_let_loop       -> while let
  * 1x useless_conversion   -> drop redundant .into_iter()

rust-toolchain.toml

@@ -0,0 +1,4 @@
+[toolchain]
+channel = "1.95"
+components = ["rustfmt", "clippy"]
+profile = "minimal"

src-tauri/src/proxy/providers/transform_responses.rs

@@ -203,6 +203,7 @@ pub(crate) fn map_responses_stop_reason(
         {
             "max_tokens"
         }
+        "incomplete" => "end_turn",
         _ => "end_turn",
     })
 }