Add Persian (fa) language support

[citoreh]

Summary

• Adds webui/i18n/fa.json with a full Persian translation of all 418 required UI strings, matching the same coverage tier as the other secondary locales (az, ca, de, es, fr, id, it, ko, pt, ru, tr, vi)
• Adds fa-IR to the video script generation language options in webui/Main.py, so users can also generate video scripts in Persian
• Adds fa to SECONDARY_LOCALES in test/services/test_webui_i18n.py so coverage, format-placeholder, and markdown-URL checks run against it going forward
• Adds README-fa.md, a full Persian translation of README-en.md, following the existing en/ja localization pattern (links, image sources, code blocks, and the in-page anchor preserved/adapted to match), and updates the language switcher in README.md, README-en.md, and README-ja.md to link to it

Test plan

• pytest test/services/test_webui_i18n.py -v — all 16 tests / ~11k subtests pass, including coverage, duplicate-key, format-placeholder, and markdown-URL preservation checks against the new locale
• Verified via utils.load_locales / utils.resolve_ui_language that the fa locale is discovered and resolves correctly from fa / fa-IR browser locales
• Verified every link/image URL in README-fa.md matches README-en.md exactly (only expected differences: the self-referencing switcher link, and the in-page anchor updated to match the translated heading)
• Visual/manual check of the WebUI with Persian selected (not done — no browser access in this environment; Persian is RTL and this app currently has no RTL layout support, same as all other non-Latin-script secondary locales added so far)

🤖 Generated with Claude Code

[harry0703]

Thanks for the substantial work on Persian support, including the locale tests and README translation. I appreciate the clear test notes.

Before merging, I'd like to check the WebUI with Persian selected, particularly right-to-left text, alignment, and any clipping in the main form and settings dialog. The full README translation also needs a wording and consistency pass. I'll review those locally and follow up with any concrete issues; no need to make speculative changes in the meantime.

Thanks again for the contribution!