feat(ux): implement dedicated 14-in-1 tools hub and smart next-action workflow engine

[gzz727007]

🦭 Pull Request Description

Summary of Changes

This pull request implements a dedicated 14-in-1 tools hub on the root route and a centralized, context-aware next-action workflow engine:

1. Dedicated 14-in-1 Tools Hub (HomeView.vue):

   • Replaced root / automatic redirect to /merge-pdf with a clean, privacy-first 14-tool matrix homepage.
   • Organized tools into 3 functional suites: Popular Essentials (6 tools), Privacy & Security (4 tools), and Conversion & Automation (4 tools).
   • Enriched card visual density with inline icons and titles, 100% individual badge coverage, dual feature pills per card, and hover lift animations.
   • Streamlined desktop navigation: removed redundant "All Tools" tab from the center bar; clicking the brand logo PDFSeal on desktop or mobile smoothly returns to /.

2. Context-Aware Next-Action Workflow Engine (workflowStrategy.js & NextActionBanner.vue):

   • Centralized recommendation strategy resolver without duplicating code across tool components.
   • Graceful silence for ZIP archives: completely suppresses the relay banner when output is a .zip bundle (pdf_to_image, multi-file split), preserving a minimal delivery card.
   • Size-aware threshold (> 10MB): automatically flags oversized deliverables and prioritizes Compress PDF to prevent email attachment limits.
   • Contextual semantic chaining:
     • merge (<= 10MB): Prioritizes sequential re-pagination (Page Number) to fix fragmented chapters; secondary actions offer Organize, Sign, and Compress (omits premature encryption).
     • organize / image_to_pdf / split (single PDF): Re-paginates sequential page numbers.
     • sign / watermark / sanitize: Recommends AES-256 permission lock to prevent post-signing tampering.
     • redact: Recommends metadata stripping (Sanitize) for a closed privacy loop.
     • unlock: Recommends Organize and Split after restrictions are removed.

3. Internationalization & Testing:

   • Added and synchronized 34 new translation keys across all 5 supported languages (en, zh, de, es, fr).
   • Added unit test suites tests/homeView.test.js and tests/workflowStrategy.test.js.
   • Verified that all 35 test files and 224 unit/integration tests pass 100%.

Type of Change

• 🐛 Bug fix (non-breaking change fixing an issue)
• ✨ New feature (non-breaking change adding functionality)
• ⚡ Performance optimization (rendering, memory, or bundle size)
• 🎨 UI / UX refinement
• 🌍 Internationalization / Translations (new or updated language)
• 📝 Documentation update (README, Guides, Comments)
• 🧪 Test suite enhancement

---

🛡️ Privacy & Quality Checklist

• 100% Client-Side Invariant: All code runs strictly in the browser RAM / WebAssembly. No user documents or telemetry data are ever sent over the network.
• Automated Tests: I have verified that all existing tests pass (npm test).
• New Tests Added: I have added unit or E2E tests covering new algorithmic behavior (if applicable).
• Responsive & Cross-Browser: Verified that UI works smoothly across desktop and mobile screens.
• Self-Review: I have performed a self-review of my own code and removed unnecessary console.log statements.

---

Related Issues

Closes #