Simplify DeckMD with a guided symptom flow

[deucebucket]

What changed

• replaces the wall of checks with six broad starting categories
• nests the 12 primary symptoms under those categories, with only 1–3 choices per category
• asks one focused follow-up group at a time
• disables contradictory answers and explains why they are unavailable
• preserves all 128 diagnostic facts behind a grouped, searchable Browse all checks fallback
• limits the first result view to the three strongest matches
• keeps selected facts removable and the URL/share summary workflow intact
• adds responsive mobile behavior, keyboard interaction, and a local favicon
• updates the README so DeckMD is described as the broad diagnostic tool it is

The design stays within DeckDoc's existing dark field-instrument aesthetic. Its distinctive element is still the signal constellation, now revealed only after useful symptom input instead of competing with the opening decision.

No outside component reference was used; this is an information-architecture refinement of the existing static HTML/CSS/JavaScript GitHub Pages app.

Validation

• all 27 repository tests pass
• DeckMD schema validates 6 categories, 12 symptoms, 128 facts, 27 contradiction rules, and 15 ranked branches
• local link validator passes across 31 Markdown files and the site
• JavaScript syntax checks pass
• Firefox/Selenium interaction pass on desktop and mobile:
  • category nesting
  • pointer and keyboard controls
  • contradiction pruning
  • grouped advanced search
  • URL state
  • responsive layout

Refs #23