feat(skills): add typography and motion principles, fix validate $& bug (#228)

Add two new skill reference files that address measured LLM composition failures:

- fonts.md: Typography principles — banned fonts, guardrails for violations
  (pairing two sans-serifs, defaulting to 400/700 weight), and guidance the LLM
  genuinely doesn't apply without being told (register switching, tension as
  meaning, easing direction as emotion). Includes Google Fonts API discovery
  script with 7-category multi-strategy query.

- motion-principles.md: Motion design principles — guardrails for same-ease and
  same-speed defaults, y-axis entrance monotony, and guidance for build/breathe/
  resolve scene structure, hard cuts as intentional transitions, visual
  composition rules for video-not-web density.

Both files validated against baseline evals: 3 compositions created without
guidance confirmed the LLM reaches for banned fonts (Inter, Cormorant Garamond,
Playfair Display, Roboto Condensed), uses power2.out on 45-72% of tweens,
enters 80%+ of elements from y-axis, and pairs multiple sans-serifs.

Also:
- Fix validate.ts $& replacement bug (runtime source containing $& caused
  String.prototype.replace to re-insert the matched <script src=""> tag)
- Clean up font loading guidance across skills (compiler embeds automatically)
- Update house-style.md to reference fonts.md

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/hyperframes/references/transitions/catalog.md

@@ -8,7 +8,7 @@ These cause real bugs if violated.
 
 **Scene visibility:** Scene 1 visible by default (no `opacity: 0`). Scenes 2+ have `opacity: 0` on the CONTAINER div. GSAP reveals them. No visibility shim (`timedEls`).
 
-**Iframe compatibility:** No external font links (`<link>` to Google Fonts, `@import`). They block sandboxed iframes. Use system fonts.
+**Fonts:** Just write the `font-family` you want — the compiler embeds supported fonts automatically via `@font-face` with inline data URIs. No need for `<link>` tags or `@import`. Works in all contexts including sandboxed iframes.
 
 **Element structure:** No `class="clip"` on scene divs in standalone compositions. Only the root div gets `data-composition-id`/`data-start`/`data-duration`.
 
@@ -57,7 +57,7 @@ Read [shader-setup.md](./shader-setup.md) for the full setup code these rules ap
         height: 1080px;
         overflow: hidden;
         background: #000;
-        font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
+        font-family: "YOUR FONT", sans-serif; /* compiler embeds supported fonts automatically */
       }
       .scene {
         position: absolute;