feat(targets): add multi-target CLI adapter system (Droid support)

Implement target adapter pattern enabling CCS CLI to support multiple backend targets
(Claude, Droid) via pluggable adapters. Core additions:

- TargetAdapter interface for pluggable target implementations
- ClaudeAdapter and DroidAdapter concrete implementations
- Target registry (singleton Map-based storage)
- Target resolver with precedence: --target flag > per-profile config > busybox detection
- Droid config manager with atomic writes and file locking to ~/.factory/settings.json
- Droid binary detector to validate runtime environment
- Adapter dispatch integrated into ccs.ts main execution flow
- ccsd busybox alias for seamless Droid invocation
- --target flag documentation in help
- Session tracking enriched with target metadata
- Dashboard target badge for visual identification

Testing:
- 43 unit tests covering resolver, registry, config manager, and adapters
- Full coverage of target detection logic and edge cases

Documentation:
- Refactored system-architecture.md into modular docs/system-architecture/ subdirectory
- Updated code-standards.md with target adapter guidelines
- Updated codebase-summary.md with architecture overview
- Updated maintainability baseline (33.8% → 35.2%)

This establishes extensible foundation for multi-target support without breaking
existing Claude workflows. Droid adapter is production-ready but defaults to Claude
for backward compatibility.

src/commands/help-command.ts

@@ -301,11 +301,17 @@ Run ${color('ccs config', 'command')} for web dashboard`.trim();
   // Flags
   printSubSection('Flags', [
     ['--config-dir <path>', 'Use custom CCS config directory'],
+    ['--target <cli>', 'Target CLI: claude (default), droid'],
     ['-h, --help', 'Show this help message'],
     ['-v, --version', 'Show version and installation info'],
     ['-sc, --shell-completion', 'Install shell auto-completion'],
   ]);
 
+  // Aliases
+  printSubSection('Aliases', [
+    ['ccsd <profile> [args]', 'Shorthand for: ccs <profile> --target droid'],
+  ]);
+
   // Configuration
   printConfigSection('Configuration', [
     ['Config File:', isUnifiedMode() ? `${dirDisplay}/config.yaml` : `${dirDisplay}/config.json`],