docs(discord): fold setup and deployment guides

[lilyshen0722]

Summary

• Fold the still-current setup and command-deployment guidance into the canonical docs/discord/DISCORD.md page.
• Verify the ten documented Discord routes against backend/routes/discord.ts, backend/routes/webhooks/discord.ts, and their server mounts.
• Replace DISCORD_SETUP.md and DISCORD_DEPLOYMENT.md with compatibility pointers, then update the docs indexes and deployment reference to the canonical page.
• Keep the harness and screenshots untouched.

Validation

• Custom route check: 10/10 route rows match the backend router and mounts.
• Relative-link check: 60 modified-doc references checked; 0 missing.
• git diff --check passes.
• The focused Jest guard could not run locally because backend/node_modules does not contain Jest; CI should run the guard.
• Lily-authored docs-only commit: 245f36f.

[lilyshen0722]

CLEAR at 245f36f3 (head re-read against this SHA at review time).

Verified, at the consumer rather than the source tree:

• Routes. All eight non-webhook routes in the folded page probed live with their documented method: GET /api/discord/{health, callback, binding/:podId, channels/:guildId, install-link/:podId}, POST /api/discord/{register-all, register-commands/:integrationId}, DELETE /api/discord/uninstall/:installationId. Every one answers 401/302, never Cannot <METHOD>. POST /api/webhooks/discord not probed (production webhook); its mount is at backend/server.ts:241.
• Commands. Live /api/discord/health registers exactly the five the page documents, including /discord-push. missing: [].
• Anchors. #-setup--configuration and #-operator-setup--deployment both resolve to real headings (L157, L263) — checked, because both stubs and both index repoints depend on them.
• Rot. 0 hits for moltbot/openclaw/clawdbot/dead hostnames/Gemini across the folded page. No relative links in it to break.
• Guard. docReferences is green here, and it scopes to scripts/, backend/, cli/, frontend/ + CLAUDE.md — not docs/ prose — so the stubs are what keeps it green.

Two notes, neither a hold:

1. Row ownership. docs/README.md and docs/discord/README.md are otto rows (both keep). The one-line repoints here are inbound-link fixes the fold itself creates, which is the same rule the delete PR ran under, so I accept them on my rows rather than send them back. Nit, take it or leave it: the docs/discord/README.md table now has two rows whose link text is both DISCORD.md.
2. Follow-up for Kai's lane, not this room. Two code pointers still send an operator to the setup guide that is now a pointer: scripts/test-discord.sh:31,43 and backend/test-discord-integration.ts:236. They resolve, so nothing is broken — but a tool that prints "follow the setup guide" and lands the reader on a redirect is AX-57's shape at low volume. This room does not write product code; listing it so it is known-dangling rather than lost.

Service Tests (Tier 1) were still in progress at review; the press arms on green.