fix(clippy): fix Rust nightly clippy lints

Fix two new lints enforced by Rust nightly:

**1. clippy::useless_borrows_in_formatting (auth.rs:57)**
- Changed: `&pkce.code_challenge` → `pkce.code_challenge`
- format!() automatically borrows, explicit & is redundant

**2. clippy::unnecessary_sort_by (confluence_search.rs:131)**
- Changed: `sort_by(|a, b| f(a).cmp(&f(b)))` → `sort_by_key(|a| f(a))`
- sort_by_key is more idiomatic and efficient (computes key once per element)

**Why Nightly Enforces This:**
Rust nightly has stricter clippy lints than stable.
These weren't errors in stable rust but are caught in nightly.

**Verified:**
✅ cargo clippy passes (0 warnings)
✅ cargo test passes (308 tests)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src-tauri/src/integrations/auth.rs

@@ -54,7 +54,7 @@ pub fn build_auth_url(
         urlencoding_encode(client_id),
         urlencoding_encode(redirect_uri),
         urlencoding_encode(scope),
-        &pkce.code_challenge,
+        pkce.code_challenge,
     )
 }
 

src-tauri/src/integrations/confluence_search.rs

@@ -128,7 +128,7 @@ pub async fn search_confluence(
         }
     }
 
-    all_results.sort_by(|a, b| canonicalize_url(&a.url).cmp(&canonicalize_url(&b.url)));
+    all_results.sort_by_key(|a| canonicalize_url(&a.url));
     all_results.dedup_by(|a, b| canonicalize_url(&a.url) == canonicalize_url(&b.url));
 
     Ok(all_results)