refactor(services): split monolithic provider.rs into modular structure

Split the 1446-line services/provider.rs into 5 focused modules:

- gemini_auth.rs (250 lines): Gemini authentication type detection
  - PackyCode, Google OAuth, and generic provider detection
  - Security flag management for different auth types

- live.rs (300 lines): Live configuration operations
  - LiveSnapshot backup/restore
  - Reading and writing live config files
  - Sync current provider to live config

- usage.rs (150 lines): Usage script execution
  - Query and test usage scripts
  - Format usage results
  - Validate usage script configuration

- endpoints.rs (80 lines): Custom endpoints management
  - CRUD operations for provider custom endpoints
  - Last-used timestamp tracking

- mod.rs (650 lines): Core provider CRUD and service facade
  - ProviderService struct with all public methods
  - Provider add/update/delete/switch operations
  - Claude model key normalization
  - Credential extraction and validation

All 107 tests pass. This improves maintainability by:
- Separating concerns into cohesive modules
- Making Gemini-specific logic easier to find and modify
- Reducing cognitive load when working on specific features

src-tauri/src/services/provider/endpoints.rs

@@ -0,0 +1,98 @@
+//! Custom endpoints management
+//!
+//! Handles CRUD operations for provider custom endpoints.
+
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::app_config::AppType;
+use crate::error::AppError;
+use crate::settings::CustomEndpoint;
+use crate::store::AppState;
+
+/// Get custom endpoints list for a provider
+pub fn get_custom_endpoints(
+    state: &AppState,
+    app_type: AppType,
+    provider_id: &str,
+) -> Result<Vec<CustomEndpoint>, AppError> {
+    let providers = state.db.get_all_providers(app_type.as_str())?;
+    let Some(provider) = providers.get(provider_id) else {
+        return Ok(vec![]);
+    };
+    let Some(meta) = provider.meta.as_ref() else {
+        return Ok(vec![]);
+    };
+    if meta.custom_endpoints.is_empty() {
+        return Ok(vec![]);
+    }
+
+    let mut result: Vec<_> = meta.custom_endpoints.values().cloned().collect();
+    result.sort_by(|a, b| b.added_at.cmp(&a.added_at));
+    Ok(result)
+}
+
+/// Add a custom endpoint to a provider
+pub fn add_custom_endpoint(
+    state: &AppState,
+    app_type: AppType,
+    provider_id: &str,
+    url: String,
+) -> Result<(), AppError> {
+    let normalized = url.trim().trim_end_matches('/').to_string();
+    if normalized.is_empty() {
+        return Err(AppError::localized(
+            "provider.endpoint.url_required",
+            "URL 不能为空",
+            "URL cannot be empty",
+        ));
+    }
+
+    state
+        .db
+        .add_custom_endpoint(app_type.as_str(), provider_id, &normalized)?;
+    Ok(())
+}
+
+/// Remove a custom endpoint from a provider
+pub fn remove_custom_endpoint(
+    state: &AppState,
+    app_type: AppType,
+    provider_id: &str,
+    url: String,
+) -> Result<(), AppError> {
+    let normalized = url.trim().trim_end_matches('/').to_string();
+    state
+        .db
+        .remove_custom_endpoint(app_type.as_str(), provider_id, &normalized)?;
+    Ok(())
+}
+
+/// Update endpoint last used timestamp
+pub fn update_endpoint_last_used(
+    state: &AppState,
+    app_type: AppType,
+    provider_id: &str,
+    url: String,
+) -> Result<(), AppError> {
+    let normalized = url.trim().trim_end_matches('/').to_string();
+
+    // Get provider, update last_used, save back
+    let mut providers = state.db.get_all_providers(app_type.as_str())?;
+    if let Some(provider) = providers.get_mut(provider_id) {
+        if let Some(meta) = provider.meta.as_mut() {
+            if let Some(endpoint) = meta.custom_endpoints.get_mut(&normalized) {
+                endpoint.last_used = Some(now_millis());
+                state.db.save_provider(app_type.as_str(), provider)?;
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Get current timestamp in milliseconds
+fn now_millis() -> i64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_millis() as i64
+}