feat: add Docker build support with local cache and custom image

Add comprehensive Docker build infrastructure for both CLI and GUI
builds with dependency caching and optimized build times.

Changes:

Docker Infrastructure:
- Add Dockerfile with pre-installed GUI build dependencies
  - Base: rust:latest
  - Includes: libdbus-1-dev, pkg-config, libxkbcommon-dev, wayland, xcb
  - Image size: 2.34GB (600MB compressed)
- Add .dockerignore to optimize build context
  - Excludes: target/, bin/, .cache/, .git/, docs/

Makefile:
- Add docker-image target to build custom Docker image
- Add build-docker target for CLI builds using Docker
  - Uses local .cache directory for cargo registry and git cache
  - Mounts as user to avoid permission issues
  - Build time: ~12s (with cache)
- Add gui-build-docker target for GUI builds using Docker
  - Uses same cache as CLI builds
  - No runtime dependency installation needed
  - Build time: ~54s (with cache)
- Update help documentation for new Docker targets

Build Cache:
- Add .cache directory for persistent cargo package cache
  - Separate subdirectories: .cache/registry and .cache/git
  - Shared between CLI and GUI builds
  - Avoids re-downloading packages on each build
  - Add .cache/ to .gitignore

CLAUDE.md:
- Enhanced architecture documentation with detailed patterns
- Add layered architecture flow diagrams
- Document critical architectural patterns:
  - Trait-based abstraction for testing without hardware
  - Validated domain types pattern
  - Error hierarchy and propagation
  - No-panic guarantee in library code
  - Dry-run pattern for safe testing
- Add GUI architecture section (Elm Architecture/TEA pattern)
- Add complete workflow for adding new commands
- Add detailed file structure documentation
- Add GUI commands to quick reference

Benefits:
- Fast, reproducible builds on any system with Docker
- No need to install Rust or build dependencies on host
- Consistent build environment across machines
- Package cache persistence reduces build times
- Clean separation of build dependencies

Author: mqasimca

.dockerignore

@@ -0,0 +1,29 @@
+# Build artifacts
+target/
+bin/
+.cache/
+completions/
+
+# Git
+.git/
+.gitignore
+
+# Editor/IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Documentation
+docs/
+screenshots/
+*.md
+LICENSE
+
+# Project specific
+*plan

.gitignore

@@ -2,6 +2,7 @@
 /target/
 /bin/
 /completions/
+/.cache/
 
 # Editor/IDE
 .idea/