feat(a11y): add a Text size control and an OpenDyslexic font option (#4210)

* feat(a11y): add a Text size control and an OpenDyslexic font option

Text size: a Theme > Font & Layout control (Default / Larger) that scales the whole UI via CSS zoom, so the many hard-coded px sizes scale too (density only moves the root font-size). Stored globally so it persists across theme switches; applied early in the boot script to avoid a flash. OpenDyslexic: a dyslexia-friendly self-hosted font (SIL OFL 1.1), bundled as woff2 alongside Fira Code/Inter and wired into the Font select. Reuses the existing density/font pattern end to end; no new colours, spacing, or component styles.

* fix(a11y): keep modals on-screen at Larger text size

Inline vh heights on .modal-content overrode the ui-scale-125 max-height
compensation, so Cookbook (and the email/doc/skills/PDF modals) overflowed
the viewport at 125% — pushing the header and close button off-screen.
Let the compensation own those heights.

* fix(a11y): keep PDF export modal at its original 86vh on Default size

static/js/skills.js

@@ -1802,7 +1802,7 @@ async function _showSkillSource(name) {
   wrap.className = 'modal';
   wrap.style.display = 'block';
   wrap.innerHTML = `
-    <div class="modal-content" style="max-width:760px;max-height:85vh;display:flex;flex-direction:column">
+    <div class="modal-content" style="max-width:760px;display:flex;flex-direction:column">
       <div class="modal-header">
         <h4>SKILL.md — <code>${esc(name)}</code></h4>
         <span style="flex:1"></span>