feat(website): mobile touch controls for the Parthenon example

[apresmoi]

Adds a touch game controller to the /examples/parthenon page so the first-person walkthrough is usable on phones (previously you could open FPV on mobile but couldn't walk or turn).

Everything in the controller is rendered by glyphcss itself — the joystick and buttons are ASCII, matching the scene.

What's new

• Glyph joystick — a dim-cyan ring + bright knob rendered as its own glyph scene at a finer density than the temple. Drives synthetic WASD into the FPV controls (which walk without pointer-lock, which touch can't grant). Hand-rolled pointer-drag with window-level release + blur/visibility safety resets, so the stick never sticks when your finger leaves the pad.
• Drag-to-look — since touch can't grab pointer-lock, dragging anywhere on the temple turns the camera (mirrors the FPV control's deriveTarget). Twin-stick: left thumb walks, a second drag looks.
• Spinning cube buttons — M (previews the style you'll switch to: matrix ↔ marble cube) and C (label toggles FPV/ORBIT), each a themed, animated glyph cube.
• Sidebar key hints (desktop) — M/C chips and a FPV legend (WASD / Space / Esc) that appears only while walking.
• Touch detection — the pad is gated by JS (maxTouchPoints + coarse-pointer + mobile UA), not a CSS media query (many phones report hover: hover). ?pad=1 / ?pad=0 force it on/off for testing.

Notes

• Website-only — no library/API changes, so no React/Vue mirror needed. The joystick + buttons flow through one page-local makeHudLayer(host, { cam, spin, onDrag/onEnd }) helper — a deliberate prototype of a future GlyphHudLayer (fixed per-layer camera + screen anchor + pointer routing) we can promote into glyphcss later.
• Desktop behavior is unchanged (pad hidden; keyboard shortcuts + click-to-lock mouselook intact).