feat(conference-map): 2026 floor plans with tappable per-floor cards

[JacobCoffee]

Summary

• Replaces the inline scroll of three floor PNGs on the Floor Plans tab with a card list (one per LBCC floor / area). Each card opens a fullscreen, zoomable modal on tap.
• Thumbnails (~50–80 KB each) load up front for a fast tab; the high-res 2200 px JPG (~270–430 KB) is only fetched when the user opens that floor's modal.
• Modal uses `pinch-zoom` with `limitZoom="original image size"` so double-tap / pinch / wheel zoom to native resolution instead of the library's default 3× cap.

Floor plans

Images extracted from the 2026 marked-up LBCC PDFs from PyCon US:

1. Concourse Level — Tutorials, Talk Track, Registration, Expo entry
2. Upper Level — Talk Track, Sponsor Presentations, Speaker Ready, Summits
3. Arena & Exhibit Halls — Keynotes, Lightning Talks, Expo Hall, Job Fair
4. Seaside Meeting Rooms — Sprints, Open Spaces, PyLadies Auction, Web Assembly Summit

Removes the now-unused `floor-{two,three,four}.png` (~1.7 MB).

Test plan

• `make serve`, open the side menu → Conference Center, ensure the Floor Plans segment is selected by default.
• Verify all 4 cards render with thumbnails + the right titles/subtitles.
• Tap each card; modal opens with the matching title and full image.
• In the modal: double-tap to zoom, pinch / wheel-zoom, drag to pan.
• Close button (top-left X) dismisses the modal cleanly.
• Confirm the 3D Tour and Expo Hall segments still work and are unchanged.
• Sanity-check on iOS device (`make ios-live`) — pinch gestures, modal dismiss swipe.

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