fix(providers): use Bearer auth for Gemini CLI OAuth tokens

* fix(providers): use Bearer auth for Gemini CLI OAuth tokens

When credentials come from ~/.gemini/oauth_creds.json (Gemini CLI),
send them as Authorization: Bearer header instead of ?key= query
parameter. API keys from env vars or config continue using ?key=.

Fixes #194

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor(gemini): harden OAuth bearer auth flow and tests

* fix(gemini): granular auth source tracking and review fixes

Build on chumyin's auth model refactor with:
- Expand GeminiAuth to 4 variants (ExplicitKey/EnvGeminiKey/EnvGoogleKey/
  OAuthToken) so auth_source() uses stored discriminant without re-reading
  env vars at call time
- Add is_api_key()/credential() helpers on the enum
- Upgrade expired OAuth token log from debug to warn
- Add tests: provider_rejects_empty_key, auth_source_explicit_key,
  auth_source_none_without_credentials

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* style: apply rustfmt to fix CI lint failures

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: root <root@instance-20220913-1738.vcn09131738.oraclevcn.com>
Co-authored-by: argenis de la rosa <theonlyhennygod@gmail.com>

src/identity.rs

@@ -183,8 +183,8 @@ pub fn load_aieos_identity(
 
     // Fall back to aieos_inline
     if let Some(ref inline) = config.aieos_inline {
-        let identity: AieosIdentity = serde_json::from_str(inline)
-            .context("Failed to parse inline AIEOS JSON")?;
+        let identity: AieosIdentity =
+            serde_json::from_str(inline).context("Failed to parse inline AIEOS JSON")?;
 
         return Ok(Some(identity));
     }
@@ -544,10 +544,7 @@ mod tests {
 
         // Check motivations
         let mot = identity.motivations.unwrap();
-        assert_eq!(
-            mot.core_drive.unwrap(),
-            "Help users accomplish their goals"
-        );
+        assert_eq!(mot.core_drive.unwrap(), "Help users accomplish their goals");
 
         // Check capabilities
         let cap = identity.capabilities.unwrap();