ask-forum: promote to a full skill + wire into skill-first routing

Add .claude/skills/ask-forum/SKILL.md (usage contract, correlation model,
forum-only scope, access/permissions) and route to it from CLAUDE.md
(skill-first covered domains) + SKILL_ROUTING.md, so sessions invoke the
skill instead of hand-rolling the Discord API — the footgun that produced a
broken background wait. Capture that footgun as memory
feedback_background_task_no_ampersand (run_in_background, never a shell &).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/CLAUDE.md

@@ -44,7 +44,9 @@ production, data-loss. Detail: EXTENDED + `.claude/OLLAMA.md`.
   records (e.g. Syncro tickets/invoices) reach a human for cleanup. **Syncro billing/invoicing
   ALWAYS runs through `/syncro` (or `/syncro-emergency-billing`) — no exceptions.** Same for
   other covered domains: credentials → `vault`, RMM actions → `/rmm` (+ `rmm-search` to find a
-  host), M365 → `remediation-tool`, etc. Knowing the API is NOT a reason to bypass the skill —
+  host), M365 → `remediation-tool`, asking a human a question/decision in Discord (get their
+  reply back in-session) → `ask-forum` (never hand-roll the Discord API — that footgun cost us
+  a broken background wait), etc. Knowing the API is NOT a reason to bypass the skill —
   the memory rules (e.g. [[feedback_syncro_billing]]) describe what the SKILL does, not a license
   to free-hand it. Reach for raw API ONLY when no skill fits or the skill genuinely cannot do it
   — and say so explicitly when you do. Mistakes here go to `errorlog.md` (`--correction`).