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/channels/mod.rs

@@ -21,10 +21,10 @@ pub use traits::Channel;
 pub use whatsapp::WhatsAppChannel;
 
 use crate::config::Config;
+use crate::identity;
 use crate::memory::{self, Memory};
 use crate::providers::{self, Provider};
 use crate::util::truncate_with_ellipsis;
-use crate::identity;
 use anyhow::Result;
 use std::sync::Arc;
 use std::time::{Duration, Instant};
@@ -205,7 +205,9 @@ pub fn build_system_prompt(
                 }
                 Err(e) => {
                     // Log error but don't fail - fall back to OpenClaw
-                    eprintln!("Warning: Failed to load AIEOS identity: {e}. Using OpenClaw format.");
+                    eprintln!(
+                        "Warning: Failed to load AIEOS identity: {e}. Using OpenClaw format."
+                    );
                     load_openclaw_bootstrap_files(&mut prompt, workspace_dir);
                 }
             }
@@ -534,7 +536,13 @@ pub async fn start_channels(config: Config) -> Result<()> {
         ));
     }
 
-    let system_prompt = build_system_prompt(&workspace, &model, &tool_descs, &skills, Some(&config.identity));
+    let system_prompt = build_system_prompt(
+        &workspace,
+        &model,
+        &tool_descs,
+        &skills,
+        Some(&config.identity),
+    );
 
     if !skills.is_empty() {
         println!(