fix: resolve build failures, security issues, and architectural improvements

Critical Fixes:
- Remove missing sw_combine.js from prebuild script and all documentation
- Remove missing test-safety-check.sh from test:all script
- Add build:web:build alias to fix docker commands
- Fix syntax errors in validate-critical-files.sh script

Security:
- Fix Electron path traversal vulnerability in export-data-to-downloads handler
  - Sanitize file names using basename() to prevent directory traversal
  - Enforce allowed file extensions (.json, .txt, .csv, .md, .log)
  - Add validation for empty names, path separators, and length limits

Architecture Improvements:
- Add queue size guard to CapacitorPlatformService (max 1000 operations)
  - Fail-fast when queue is full to prevent memory exhaustion
  - Add warning at 80% capacity
  - Add getQueueTelemetry() method for monitoring queue health
  - Track peak queue size for diagnostics

- Standardize environment variable usage in PlatformServiceFactory
  - Prefer import.meta.env.VITE_PLATFORM (standard Vite pattern)
  - Maintain backward compatibility with process.env fallback

Documentation:
- Clarify PWA status: remove misleading VitePWA comments
- Update BUILDING.md to reflect removed sw_combine.js step
- Update build-arch-guard.sh to remove sw_combine.js from protected files

All changes maintain backward compatibility and improve code quality.

doc/README-BUILD-GUARD.md

@@ -105,8 +105,7 @@ Build Scripts:
 ├── electron/**            # Electron build files
 ├── android/**             # Android build configuration
 ├── ios/**                 # iOS build configuration
-├── sw_scripts/**          # Service worker scripts
-└── sw_combine.js          # Service worker combination
+└── sw_scripts/**          # Service worker scripts
 
 Deployment:
 ├── Dockerfile             # Docker configuration