feat: event-app-space-report skill (per-event completion report) - #3038

What

Adds a reusable skill + script that produces a per-event tutorial-completion report for the tutorials-ims platform from an app-space URL or eventId.

• .claude/skills/event-app-space-report/SKILL.md — invoke with an app-space URL (…/app-space/?eventId=NNN) or bare eventId.
• scripts/event-report.mjs — standalone, read-only, prod-guarded ESM script. Reuses srv/lib/event-path-buckets.js so Track numbers match the live app-space page. Runnable outside the skill: cds bind --exec -- node scripts/event-report.mjs <eventId> [--json].

Report sections

1. Completions by Track — total + per-Track count/share (Track = CompletionPaths.name; FK-first tutorial resolution; windowed COMPLETED/SUPERSEDED).
2. Abandoned tutorials — top-abandonees list, computed stop-pattern summary, per-tutorial median stop-step with "% through", per-step drop histogram.
3. Completer email domains — per-domain users/completions/avg, multi-domain org rollup (ORG_DOMAIN_MAP: NTT Data, EY), most-engaged table + prose callout.
4. SAP vs external — @sap.com vs rest.

Key correctness decisions

• Scoped by date window (completionDate ∈ [Events.startDate, endDate]), never TaskRecords.event_ID (NULL on normal completions).
• FK-first resolution (CompletionPathItems.tutorial_ID → Tutorials.legacyId); manually-authored prod event missions leave taskLegacyId NULL (Not possible to navigate back up from tutorial to mission #1866).
• Sections 3–4 reconcile with §1's hero total (same all-windowed set); (unknown)/anonymized emails excluded from the SAP-vs-external split.
• Abandonment uses modifiedAt-in-window; stop-step is an attemptNumber-scoped approximation (documented in SKILL.md).

Testing

• 22/22 unit tests (test/scripts/event-report*.test.js, in-memory SQLite).
• Verified live against PROD for ASUG Tech Connect (eventId 10000003): resolves event + window + mission, all four sections render, Track totals consistent with computePathBuckets.

Safety

Read-only (SELECT/CQL only); refuses to run unless cf target space is prod. No writes, no deploy. The script lives in the repo so it's reusable independently of the skill.