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/en/default.json

@@ -426,5 +426,11 @@
   "tor_author_flag_label": "This user is on Tor",
   "copy_share_link": "Copy share link",
   "directory_submit_board": "Submit Your Board",
-  "all_subtitle": "The highest-scoring board from each directory"
+  "all_subtitle": "The highest-scoring board from each directory",
+  "post_form_math_tags_prompt": "Use <tex>TeX</tex> with [math] tags for inline and [eqn] tags for block equations.",
+  "post_form_math_right_click_prompt": "Right-click equations to view the source.",
+  "tex_preview_title": "<tex>TeX</tex> Preview",
+  "tex_preview_protip": "Use [math][/math] tags for inline, and [eqn][/eqn] tags for block equations.",
+  "tex_preview_input_label": "TeX source",
+  "preview_tex_equations": "Preview TeX equations"
 }