docs: Update README and add CHANGELOG for v1.2.0

Added v1.2.0 release notes documenting CLI session-based Full Stack mode
and all bug fixes included in this release.

- Updated version badge to 1.2.0
- Added comprehensive v1.2.0 release notes with:
  - New CLI session-based terminal mode
  - Shell command API endpoint
  - Smart command detection
  - Bug fixes (terminal creation, XSS, memory leaks, etc.)
  - Technical details and security notes
- Created CHANGELOG.md following Keep a Changelog format

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

CHANGELOG.md

@@ -0,0 +1,74 @@
+# Changelog
+
+All notable changes to ClaudeCLI-Web will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.2.0] - 2026-01-20
+
+### Added
+- CLI session-based Full Stack mode for direct shell command execution
+- `executeShellCommand()` method to ClaudeService for spawning bash processes
+- `POST /claude/api/shell-command` API endpoint for terminal commands
+- Smart command detection to differentiate shell commands from conversational messages
+- Auto-mode switching suggestions when non-shell commands are sent in Terminal mode
+- Real-time stdout/stderr capture with event emission
+
+### Changed
+- Replaced WebContainer-based Full Stack mode with Claude Code CLI session approach
+- Simplified terminal mode architecture by removing 350KB WebContainer bundle
+- Improved session filtering with path-based project matching
+- Updated `handleWebContainerCommand()` to use CLI sessions instead of WebContainers
+
+### Fixed
+- Terminal creation failure in Full Stack mode ("Failed to create terminal" error)
+- WebContainer SharedArrayBuffer serialization errors (no longer applicable with CLI approach)
+- Session filtering showing unrelated sessions in project view
+- Memory leaks from setInterval() calls in context-panel.js and landing.js
+- XSS vulnerability in autocomplete (file names now properly escaped)
+- sendMessage() undefined errors in chat-message-enhanced.js
+- terminalManager reference errors (changed to window.terminalManager)
+
+### Removed
+- WebContainer dependency (no longer needed for Full Stack mode)
+- COOP/COEP header requirements (eliminated with CLI session approach)
+
+### Security
+- All shell command endpoints require authentication
+- Command injection protection via bash shell spawning
+- Proper HTML escaping for dynamic content in autocomplete
+
+## [1.1.0] - 2026-01-19
+
+### Added
+- HTTP polling system for terminal output
+- Terminal type selection dropdown (Standard Shell vs Claude Code CLI)
+- Debug panel for terminal troubleshooting
+- HTTP POST input and resize endpoints
+- Automatic cleanup of old terminal output (5 minutes retention)
+
+### Changed
+- Terminal output delivery from WebSocket to HTTP polling
+- Terminal command execution via HTTP POST instead of WebSocket
+
+### Fixed
+- WebSocket closure with code 1006 in nginx configurations
+- Terminal command execution failing silently
+- Race condition in `switchToTerminal()` method
+- Terminal type selector not appearing in modal
+
+## [1.0.0] - Initial Release
+
+### Added
+- Session management with real-time status tracking
+- Project organization with smart suggestions
+- WebSocket-based terminal integration
+- XML tag system for file operations
+- Obsidian vault integration
+- File browser and editor
+- Real-time chat interface
+
+[1.2.0]: https://github.rommark.dev/admin/ClaudeCLI-Web/compare/v1.1.0...v1.2.0
+[1.1.0]: https://github.rommark.dev/admin/ClaudeCLI-Web/compare/v1.0.0...v1.1.0
+[1.0.0]: https://github.rommark.dev/admin/ClaudeCLI-Web/releases/tag/v1.0.0