docs: Add comprehensive JSDoc docstrings to settings module (80% coverage)

This commit addresses CodeRabbit feedback from PR #186 by adding detailed
documentation to all public APIs in the settings module:

**Server-side documentation:**
- SettingsService class: 12 public methods with parameter and return types
- Settings types (settings.ts): All type aliases, interfaces, and constants
  documented with usage context
- Route handlers (8 endpoints): Complete endpoint documentation with request/response
  schemas
- Automaker paths utilities: All 13 path resolution functions fully documented

**Client-side documentation:**
- useSettingsMigration hook: Migration flow and state documented
- Sync functions: Three sync helpers (settings, credentials, project) with usage guidelines
- localStorage constants: Clear documentation of migration keys and cleanup strategy

All docstrings follow JSDoc format with:
- Purpose and behavior description
- Parameter documentation with types
- Return value documentation
- Usage examples where applicable
- Cross-references between related functions

This improves code maintainability, IDE autocomplete, and developer onboarding.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/server/src/routes/settings/common.ts

@@ -1,5 +1,8 @@
 /**
  * Common utilities for settings routes
+ *
+ * Provides logger and error handling utilities shared across all settings endpoints.
+ * Re-exports error handling helpers from the parent routes module.
  */
 
 import { createLogger } from "../../lib/logger.js";
@@ -8,8 +11,19 @@ import {
   createLogError,
 } from "../common.js";
 
+/** Logger instance for settings-related operations */
 export const logger = createLogger("Settings");
 
-// Re-export shared utilities
+/**
+ * Extract user-friendly error message from error objects
+ *
+ * Re-exported from parent routes common module for consistency.
+ */
 export { getErrorMessageShared as getErrorMessage };
+
+/**
+ * Log error with automatic logger binding
+ *
+ * Convenience function for logging errors with the Settings logger.
+ */
 export const logError = createLogError(logger);