docs: add Persian (fa-IR) README

[NimaHp]

Adds the Persian (fa-IR) README, in the same commit as its registration in the language switcher.

What

• .github/readmes/README.fa-IR.md, a translation of the root README
• **فارسی** appended to the switcher row in all 15 files, so the row stays symmetric: the root README plus every other locale lists this one, and none of them was touched beyond that one appended entry

Review of the incoming draft

The draft needed real cleanup before it was usable, so this is not just a copy:

• 308 [span_N](start/end_span) citation markers left by the translator, removed
• Blank lines had collapsed to 4 against 127 in the English file, which breaks lists, tables and callouts. The structure is now taken from README.md line for line
• Paths were wrong for the new location. The draft was copied from the root README, so ./.github/assets/, ./CONTRIBUTING.md and ./LICENSE would all resolve to paths that do not exist from .github/readmes/. Assets are now ../assets/, root documents ../../, the CONTRIBUTING translations ../contributing/, and the switcher points at the sibling files with فارسی bolded and English linking back to ../../README.md. Every relative link and image resolves now.
• Seven lines started with a Latin character, the product name or the language switcher, so the bidi algorithm laid those paragraphs out left to right inside a Persian document. Each carries a U+200F RIGHT-TO-LEFT MARK right before the first visible character, after the markdown syntax. Invisible, changes no link or heading.
• One Arabic yeh inside a Persian word. The yeh and teh marbuta inside العربية are left alone, since that is the native name.
• Terminology follows Translations.fa-IR.resx rather than transliteration: Copilot, PowerShell, Reflection, Hibernation, Prefetch, Registry, Task Manager, widgets as ابزارک‌ها, recycle bin as سطل بازیافتنی, scheduled tasks as وظایف زمان‌بندی‌شده, and the risk labels the app itself shows, امن / با احتیاط / تخصصی
• سوالات to سؤالات, آپدیت to به‌روزرسانی, and a stray digit removed from the Discord banner alt text

Verification

• 33 headings at matching levels against README.md, 83 links, same elements in the same order
• All 15 READMEs resolve to the same 84 distinct targets
• Zero lines left starting with a Latin character
• No unresolved relative link or image in the new file

Worth noting separately

The GPL badge here points at ../assets/gplv3.png, which resolves. The 13 existing locale files keep .github/assets/gplv3.png, which does not resolve from .github/readmes/, so their licence badge is currently broken in this repository. That is a pre-existing bug and not touched here, since it is unrelated to this contribution.

[itsfatduck]

Nice! Thank you for contributing Persian README locale!