feat: elevate dashboard with obsidian/amber theme, 5-tab explorer, and 3-tier component architecture

[Kaos599]

Summary

This PR elevates the jev-writer dashboard presentation, introduces progressive component architecture reference documentation, and enhances repository developer experience without compromising statistical rigor.

Key Changes

• Obsidian Zinc & Solar Amber Design System: Pure dark mode palette (#09090b canvas, #121215 card surface) paired with a high-readability warm solar amber accent (#fb923c). Zero emojis across all UI chrome (100% pure SVG icons).
• 5-Tab Navigation & Post Explorer:
  • Executive Overview with dynamic Key Signals & Performance Levers derived at runtime from validated findings.
  • Formats & Hooks breakdown diagnostics with sample size indicators (n).
  • Post Explorer with Cards / Table view toggle, search bar, and format filter dropdown.
  • Pre-flight Writing Blueprint prompt copy box.
  • Statistical Methodology & Verification diagnostics lab with an interactive diagnostic table.
• Micro-Interactions & Impeccable Polish: Optical padding balance, concentric border radii, scale-down press states, and tabular numerals.
• 3-Tier Component Architecture: Added skills/jev-writer/references/components.md detailing progressive UI assembly for sparse data platforms (Tier 1 text-only to Tier 3 full outcomes).
• Tests & Documentation: Expanded automated test suite in test/dashboard.test.mjs to 72 passing tests, added CLAUDE.md, and updated repository documentation.

Zero Personal Data Verification

• All copy, findings, and metrics in src/dashboard.mjs are purely dynamic from evaluated report inputs or generic benchmarks.
• Verified zero personal metrics or post data are present in the diff.
• All 72 tests pass.

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