docs: add saved repos documentation

- Create CHANGELOG entry with feature details
- Create comprehensive feature documentation (SAVED_REPOS.md)
- Add PR plan with commit strategy (PR_PLAN_SAVED_REPOS.md)
- Include quickstart guide (QUICKSTART_SAVED_REPOS.md)
- Add usage guide, API reference, architecture details
- Include troubleshooting and rollout strategy

Author: Lucifer-0612

CHANGELOG.md

@@ -0,0 +1,85 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## [Unreleased]
+
+### Added - Saved Repos Feature
+
+#### Frontend
+- **Zustand Store**: Created `useSavedProjectsStore` with localStorage persistence
+  - Stores saved repositories with key `oss_saved_repos_v1`
+  - Actions: `addProject`, `removeProject`, `toggleProject`, `clearAllSaved`, `setAll`, `isSaved`
+  - Automatic persistence across page reloads
+  
+- **UI Components**:
+  - `SaveToggle`: Star icon button in project rows to save/unsave repositories
+  - `SavedProjectsPanel`: Side panel for managing saved repos
+    - Export saved repos to JSON file
+    - Import saved repos from JSON file
+    - Clear all saved repos with confirmation
+    - View all saved repos with metadata
+  
+- **Projects Table**: Added "Save" column as first column in OSS Projects table
+- **Header Button**: Added "Saved Projects" button with count badge in projects page header
+
+#### Backend
+- **Database**: Added `saved_repos` JSONB column to `User` model (default: `[]`)
+- **Service Layer**: Created `savedReposService` with:
+  - `getSavedRepos`: Retrieve user's saved repos
+  - `mergeSavedRepos`: Merge local and server repos with conflict resolution
+  - `updateSavedRepos`: Update saved repos with add/remove/replace actions
+  - Maximum 100 saved repos per user enforcement
+  
+- **API Endpoints** (tRPC):
+  - `user.getSavedRepos`: Get user's saved repos (protected, feature flag: `FEATURE_SAVED_REPOS_DB`)
+  - `user.updateSavedRepos`: Update saved repos with merge logic (protected, feature flag: `FEATURE_SAVED_REPOS_DB`)
+  - Conflict resolution: Newer `savedAt` timestamp wins
+
+#### Shared Types
+- Created `SavedRepo` type definition in `@opensox/shared`
+- Created `SavedReposAction` and `SavedReposUpdateInput` types
+
+### Configuration
+- **Feature Flag**: `FEATURE_SAVED_REPOS_DB` - Enable/disable database sync (default: disabled)
+  - When disabled: Client-only mode with localStorage
+  - When enabled: Full sync across devices with merge logic
+
+### Migration
+- Migration file: `add_saved_repos` - Adds `saved_repos` JSONB column to User table
+
+---
+
+## How to Use
+
+### For Users
+1. Navigate to `/dashboard/projects`
+2. Click "Find projects" to search for repositories
+3. Click the star icon on any project to save it
+4. Click "Saved Projects" button to view/manage saved repos
+5. Export/import saved repos as JSON for backup
+
+### For Developers
+1. **Client-only mode** (default): Works out of the box with localStorage
+2. **Database sync mode**: Set `FEATURE_SAVED_REPOS_DB=true` in `apps/api/.env`
+3. Run migration: `cd apps/api && npx prisma migrate dev`
+4. Restart API server
+
+### API Usage (when feature flag enabled)
+```typescript
+// Get saved repos
+const savedRepos = await trpc.user.getSavedRepos.query();
+
+// Add repos
+await trpc.user.updateSavedRepos.mutate({
+  action: 'add',
+  repos: [{ id: '123', name: 'repo', url: 'https://...', savedAt: new Date().toISOString() }]
+});
+
+// Sync with merge
+await trpc.user.updateSavedRepos.mutate({
+  action: 'replace',
+  repos: serverRepos,
+  localRepos: clientRepos // Will merge and resolve conflicts
+});
+```