feat: add in-app update checker, enhance About page and project metadata

- Add AtlasUpdateChecker with GitHub Releases API integration
- Add AtlasVersionComparator for semantic version comparison
- Add AboutUpdateToolbarButton with popover update UI
- Enhance AboutFeatureView with social QR codes and layout refinements
- Add CHANGELOG.md and CODE_OF_CONDUCT.md
- Rebrand project files from Mole to Atlas for Mac
- Update build script to support version/build number injection
- Add installation guide to README
- Add bilingual localization strings for update feature
- Add unit tests for update checker and version comparator

CHANGELOG.md

@@ -0,0 +1,27 @@
+# Changelog
+
+All notable changes to Atlas for Mac will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
+
+## [Unreleased]
+
+### Added
+
+- Native macOS app with 7 MVP modules: Overview, Smart Clean, Apps, History, Recovery, Permissions, Settings
+- Recovery-first cleanup workflow — actions are reversible via Trash before permanent deletion
+- Explainable recommendations — every suggestion shows reasoning before execution
+- Bilingual UI: Simplified Chinese (default) and English, with persistent language preference
+- AtlasDesignSystem shared design tokens: brand colors (teal/mint), typography, 4pt spacing grid, continuous corner radius
+- Layered Swift Package architecture with strict dependency direction
+- XPC worker architecture for sandboxed operations
+- Privileged helper for elevated operations requiring administrator access
+- Keyboard navigation and command shortcuts for the main shell
+- Accessibility semantics and stable UI-automation identifiers
+- Native packaging: `.app`, `.zip`, `.dmg`, `.pkg` artifact generation
+- Go-based TUI tools inherited from upstream Mole: disk analyzer (`analyze`) and system monitor (`status`)
+- CI/CD: GitHub Actions for formatting, linting, testing, CodeQL scanning, and release packaging
+
+### Attribution
+
+- Built in part on the open-source [Mole](https://github.com/tw93/mole) project (MIT) by tw93 and contributors