feat: Add Forgejo CI/CD pipeline for automated builds and releases

- Create .forgejo/workflows/build.yml for automated Windows and macOS builds
- Trigger on version tags (v1.0.0, v1.0.1, etc.) or manual dispatch
- Windows job builds executable with PyInstaller
- macOS job builds DMG package
- Automatically generate SHA256 checksums for verification
- Create release on Forgejo with all artifacts
- Add FORGEJO_CI_CD_SETUP.md with complete setup guide
- Add CHANGELOG.md for version tracking
- Update DEVELOPMENT_PLAN.md with Phase 3.3 details

This enables:
- Centralized release hub on Forgejo
- Automatic distribution of builds
- Foundation for Phase 4.1 auto-update system
- Checksum-based integrity verification

DEVELOPMENT_PLAN.md

@@ -634,6 +634,71 @@ export APPLE_TEAM_ID="XXXXXXXXXX"
 
 ---
 
+### 3.3 Forgejo CI/CD Pipeline
+
+**Workflow File** (`.forgejo/workflows/build.yml`):
+- Automated builds on tag push (v1.0.0, v1.0.1, etc.)
+- Windows executable build (windows-latest runner)
+- macOS DMG build (macos-latest runner)
+- SHA256 checksum generation
+- Release creation with artifacts
+- Artifact upload to Forgejo releases
+
+**Features:**
+- ✅ Trigger on version tags
+- ✅ Manual workflow dispatch option
+- ✅ Multi-platform parallel builds
+- ✅ Automatic release generation
+- ✅ Checksum verification support
+- ✅ Integration with auto-update system (Phase 4.1)
+
+**Usage:**
+```bash
+# Create a release
+git tag -a v1.0.0 -m "Release version 1.0.0"
+git push upstream v1.0.0
+
+# Forgejo Actions automatically:
+# 1. Builds Windows executable
+# 2. Builds macOS DMG
+# 3. Generates checksums
+# 4. Creates release with artifacts
+```
+
+**Requirements:**
+- Forgejo instance with Actions enabled
+- Windows runner (for Windows builds)
+- macOS runner (for macOS builds)
+- `GITEA_TOKEN` secret configured in repository
+
+**Release Location:**
+```
+https://git.him-tools.de/HIM-public/webdrop-bridge/releases/vX.Y.Z
+├── WebDropBridge.exe
+├── WebDropBridge.exe.sha256
+├── WebDropBridge.dmg
+└── WebDropBridge.dmg.sha256
+```
+
+**Setup Guide:**
+See [FORGEJO_CI_CD_SETUP.md](FORGEJO_CI_CD_SETUP.md) for:
+- Runner installation and configuration
+- Secret setup (GITEA_TOKEN)
+- Troubleshooting
+- Integration with UpdateManager (Phase 4.1)
+
+**Acceptance Criteria:**
+- [x] Workflow file created and committed
+- [ ] Forgejo runners configured (Windows + macOS)
+- [ ] GITEA_TOKEN secret added
+- [ ] Test run: Tag v0.0.1 triggers builds
+- [ ] Release appears on Forgejo with artifacts
+- [ ] Checksums verify successfully
+
+**Status**: ✅ Workflow created | ⏳ Runners needed
+
+---
+
 ## Phase 4: Professional Features & Auto-Update (Weeks 9-12)
 
 ### 4.1 Auto-Update System with Forgejo Integration