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/documentLibrary.js

@@ -1595,7 +1595,7 @@ let _libraryArchivedView = false;   // Documents tab showing archived docs?
     modal.className = 'modal';
     modal.id = 'doclib-modal';
     modal.innerHTML = `
-      <div class="modal-content doclib-modal-content" style="width:min(640px, 92vw);max-height:85vh;background:var(--bg);">
+      <div class="modal-content doclib-modal-content" style="width:min(640px, 92vw);background:var(--bg);">
         <div class="modal-header">
           <!-- Header title + icon mirror the currently-active sub-tab (Chats /
                Documents / Research / Archive) so the user sees ONE icon at