docs: add Discord bot to READMEs, architecture, operations guides, and locales (#6513)

* docs: add Discord bot to READMEs, architecture, operations guides, and locales

* docs: address review feedback on Discord bot formatting, backup commands, and architecture

* docs(discord): fix Persian typo and literal arrows on fa/zh bot pages

Senior review of #6513, two LOW findings in the two new pages:

- fa/operations/discord-bot.mdx:30 spelled "developers" with Cyrillic
  "де" in place of Persian "ده", rendering a mixed-script word.
- Both pages copied `$\rightarrow$` from the en page. The docs site has
  no math plugin (nothing in source.config.ts, no remark-math
  installed), so the built HTML shows the literal string
  "$\rightarrow$" in every menu path. Replaced with a Unicode arrow on
  fa and zh; en and ru have carried the same since #6486 and are left
  for a separate change.

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Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

CLAUDE.md

@@ -58,8 +58,8 @@ file locations when it can answer in one hop.
 - `internal/web/` — Gin server (embeds `dist/` + `translation/`).
   - `controller/` — panel + REST API handlers; OpenAPI at /panel/api/openapi.json.
   - `service/` — business logic (InboundService, SettingService, XrayService,
-    node sync); subpackages tgbot/, email/, outbound/, panel/, integration/.
-  - `job/` — 18 cron jobs (traffic, fail2ban IP-limit, node heartbeat/sync, LDAP,
+    node sync); subpackages tgbot/, discord/, email/, outbound/, panel/, integration/.
+  - `job/` — 19 cron jobs (traffic, fail2ban IP-limit, node heartbeat/sync, LDAP,
     CPU/memory watchdogs, …); full table in `docs/architecture.md` §5.4.
   - `middleware/`, `entity/`, `global/`, `session/` (CSRF), `network/`,
     `runtime/` (master/sub-node over mTLS), `websocket/`.