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.

ui/src/components/analytics/session-stats-card.tsx

@@ -133,9 +133,16 @@ export function SessionStatsCard({ data, isLoading, className }: SessionStatsCar
                 className="flex items-center justify-between text-xs p-1.5 rounded bg-muted/30 hover:bg-muted/50 transition-colors"
               >
                 <div className="flex flex-col min-w-0 flex-1">
-                  <span className="font-medium truncate" title={session.projectPath}>
-                    {getProjectDisplayName(session.projectPath)}
-                  </span>
+                  <div className="flex items-center gap-1">
+                    <span className="font-medium truncate" title={session.projectPath}>
+                      {getProjectDisplayName(session.projectPath)}
+                    </span>
+                    {(session.target ?? 'claude') !== 'claude' && (
+                      <span className="shrink-0 px-1 py-0 text-[9px] font-medium rounded bg-purple-100 text-purple-700 dark:bg-purple-900/30 dark:text-purple-300 uppercase">
+                        {session.target}
+                      </span>
+                    )}
+                  </div>
                   <span className="text-[10px] text-muted-foreground">
                     {formatDistanceToNow(new Date(session.lastActivity), { addSuffix: true })}
                   </span>

ui/src/hooks/use-usage.ts

@@ -100,6 +100,8 @@ export interface Session {
   cost: number;
   lastActivity: string;
   modelsUsed: string[];
+  /** Target CLI used (default: 'claude') */
+  target?: string;
 }
 
 export interface PaginatedSessions {