Serve the site in English, Spanish and Arabic, add a captcha, make the message optional

- Move every route under app/[lang]; a proxy keeps English on unprefixed URLs and serves /es and /ar
- Interface strings and homepage copy per locale; content pages load a translated JSON when one exists
- Language switch in the header, hreflang alternates and a multilingual sitemap
- Right-to-left layout for Arabic with logical CSS properties, Noto Sans Arabic and no letter-spacing
- Self-hosted proof-of-work "I'm not a robot" check (no third-party account) replaces Turnstile
- The message field is optional; failed attempts refill the form instead of clearing it

scripts/convert-docs.py

@@ -7,7 +7,7 @@ Usage:
 Paragraphs that start with "> " were bold sentences in the deck and render as
 emphasised lines. Each document follows the same conventions: bold all-caps lines are eyebrows
 (when followed by a heading) or CTAs; Heading 1/2/3 give the structure.
-The output lands in src/content/pages/<slug>.json. The homepage is hand-built
+The output lands in src/content/pages/en/<slug>.json. The homepage is hand-built
 and is skipped.
 """
 
@@ -18,7 +18,7 @@ import re
 import sys
 import zipfile
 
-OUT = pathlib.Path(__file__).resolve().parent.parent / "src" / "content" / "pages"
+OUT = pathlib.Path(__file__).resolve().parent.parent / "src" / "content" / "pages" / "en"
 
 # Lines in the decks that are notes to the team, not site copy.
 DROP = [