feat(reply modal): add sci tex preview button (#1170)

* feat(sci): add 4chan-style TeX support with MathJax on /sci/

- [math]/[eqn] tags typeset with MathJax 3 (lazy chunk, only on /sci/ with math present)
- 4chan-identical config: Safe mode, left-aligned eqn, neutered \color/\newcommand macros
- TeX button in reply modal title bar opens live TeX Preview modal
- /sci/ post form rules bullets for [math]/[eqn] usage and right-click source
- MathJax context menu on right-click (Show Math As > TeX Commands)
- woff fonts served from node_modules in dev and emitted into build

* feat(sci): finish TeX support: configmacros fix, preview preload, translations, tests

- add configmacros package so the 4chan macro neutering (\color, \newcommand, ...) applies
- preload MathJax when the TeX Preview opens, like 4chan
- stable closeModal callback for the preview modal
- pre-bundle mathjax components in vite optimizeDeps to avoid dev mid-session reload
- translate the 6 new TeX keys into all 35 languages
- markdown math segment component tests + math-tags unit tests

* feat(reply modal): add sci tex preview button

* fix(tex-preview): clear MathJax bookkeeping and pending typeset on close

Addresses Cursor Bugbot: the preview output was typeset via typesetMathElement but
never passed to clearMathElement on unmount, so repeated open/close cycles kept
detached nodes in MathJax's math list. Also cancels the pending debounce timer.

* fix(reply-modal): reset TeX preview state when the reply modal closes

Addresses CodeRabbit: showTexPreview persisted across close/reopen like the
bbcode preview flags, so the TeX preview would auto-open on the next reply.

public/translations/de/default.json

@@ -407,5 +407,11 @@
   "tor_author_flag_label": "Dieser Benutzer ist auf Tor",
   "copy_share_link": "Freigabelink kopieren",
   "directory_submit_board": "Reiche dein Board ein",
-  "all_subtitle": "Das höchstbewertete Forum aus jedem Verzeichnis"
+  "all_subtitle": "Das höchstbewertete Forum aus jedem Verzeichnis",
+  "tex_preview_protip": "Verwenden Sie [math][/math]-Tags für Inline-Gleichungen und [eqn][/eqn]-Tags für Block-Gleichungen.",
+  "post_form_math_tags_prompt": "Nutze <tex>TeX</tex> mit [math]-Tags für Inline-Gleichungen und [eqn]-Tags für Block-Gleichungen.",
+  "post_form_math_right_click_prompt": "Rechtsklick auf Gleichungen zum Anzeigen der Quelle.",
+  "tex_preview_title": "<tex>TeX</tex> Vorschau",
+  "tex_preview_input_label": "TeX-Quelle",
+  "preview_tex_equations": "TeX-Gleichungen in der Vorschau anzeigen"
 }