- while nothing is shown, the whole view is a button that opens the file
  dialog ("Open a CityGML file / or drop it here")
- files can be dropped on the view at any time; an overlay shows the drop
  target, a drop replaces the shown file like choosing one
- drops elsewhere on the page are ignored instead of making the browser
  leave the viewer

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

- style.css with colour, type and spacing tokens; light grey chrome around
  the 3D view, one petrol accent for the file button, checkboxes, focus and
  a progress line along the header (replaces the native progress bar)
- header with title; the file input is a button (native input visually
  hidden, keyboard focus ring only for keyboard use)
- sidebar panel "Level of detail" with hover rows; panel message tells
  missing file, loading and files without geometry apart
- viewer: invitation to open a file while nothing is shown, mouse controls
  hint once there is geometry; viewer background #EDF3F4 matches the palette
- narrow screens: panels above the view

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

- coordinates.js: scans posList/pos text directly; plain decimals up to 15
  digits are converted exactly (integer / power of ten, bit-identical to
  parseFloat), everything else goes through parseFloat
- triangulate.js (moved out of citygml.js): triangles and quadrilaterals
  without holes are split directly, concave ones at the reflex corner;
  self-intersecting, degenerate or holed polygons and corners that coincide
  in libtess's 2D projection stay with libtess

On 156 test files vertex counts and colours are identical to before; total
area differs by at most 1.7e-6 (other diagonal of non-planar quads).
274 MB LoD2 file: 7.2 s -> 5.8 s in Node.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Zip archives are rejected again by the format check with a hint to unpack
them. Removes the zip reader, its tests and helper, the zip path in
loadFile and the zip-only layer renaming (finishLayer name, sourceName).
The archive message no longer suggests packing files as .zip. The
readStream test for always-ready streams moved to the parser tests.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

The parser only needs element names and coordinate text. The new tokenizer
finds markup with native indexOf instead of sax's per-character state
machine and slices text only while a LinearRing is read.

- 274 MB LoD2 file: 20.1 s -> 6.9 s in Node, 23.3 s -> 8.3 s in the browser
- identical output (hash over all vertex positions and colours) on 156
  test files incl. CityGML 3.0
- element names are matched case-sensitively as local names
- unterminated markup over 64 KB still fails; a truncated file still shows
  what was read
- vendor/sax.js removed

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>