feat(form-builder): admin UI completion — server filters, KPIs, resource expansion (WS-6 sessie 3c)

Closes the four production gaps that emerged from sessie 3b's admin UI.
What we ship here is final: no further rework planned before production.

Backend
- IndexFailuresRequest validates state/search/failed_at_from/failed_at_to/
  listener_class. orgIndex + platformIndex apply them via a single
  applyIndexFilters() helper. Search runs case-insensitive `LIKE` on
  exception_message; SQL wildcards in user input are escaped.
- New /kpis aggregate endpoint per scope (orgKpis, platformKpis) returns
  open / resolved_30d / dismissed_30d / total_submissions in O(1) COUNTs.
  Replaces sessie 3b's client-side bucketing of an oversized list.
- Resource expansion: organisation_name, form_schema_label,
  resolved_by_user_name, dismissed_by_user_name, exception_trace,
  retry_history[]. Eager-loading via indexEagerLoads()/detailEagerLoads()
  prevents N+1 (verified by query-count assertion in test).
- New 2026_04_28_181000 migration adds exception_trace (longtext nullable)
  to form_submission_action_failures. ApplyBindingsOnFormSubmit listener
  now captures $e->getTraceAsString() at failure time.
- New FormSubmissionActionFailureRetryAttemptResource exposes per-attempt
  data (timestamp, actor name, outcome, exception details) inside
  retry_history[]. Index payloads omit the field via whenLoaded() to keep
  list responses lean.

Frontend (apps/app)
- Types updated to mirror the expanded resource shape and the new KPI
  endpoint contract. FormFailuresKpis is now { open, resolved_30d,
  dismissed_30d, total_submissions } (server-aggregate).
- useFormFailures composable forwards all 5 server filters via
  buildIndexParams() (strips empty/whitespace). useFormFailuresKpis hits
  the dedicated /kpis endpoint per scope.
- FormFailuresTable replaces client-side bucketing with server-side
  filtering, adds listener_class + date-range filter inputs, and renames
  the 4th KPI tile to "Submissions" (was "Totaal").
- FormFailureDetail renders organisation_name + form_schema_label in the
  header, surfaces an expandable stack-trace card, names the resolved/
  dismissed actor in the timeline, and replaces the "v1 placeholder"
  retry-history card with a full per-attempt timeline.

ESLint config gap (apps/app)
- New .eslintrc.cjs adapted from the Vuexy reference, minus Vuexy-internal
  rules. `pnpm lint` now runs successfully (was previously broken — the
  package.json script referenced a missing config). The 80 baseline
  violations across the codebase are pre-existing and out of scope for
  this session.

Tests + gates
- 24 new backend tests across filter, kpis, and resource-shape suites.
  Backend: 1462 → 1486 passing, 0 → 0 failing. Larastan clean. Rector
  dry-run unchanged at 354 (pre-Task-1 baseline from f18b55b).
- 3 new vitest tests in apps/app (filter wiring, KPI endpoint, KPI tile
  values from /kpis). Vitest: 38 → 41 passing. tsc clean. Portal
  unchanged (113 vitest, tsc clean).
- 5 backfill rollback tests bumped --step counts +1 for the new migration.
- Ws6FoundationMigrationTest down/up chain now includes exception_trace
  before the parent table is restored.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dev-docs/SCHEMA.md

@@ -11,7 +11,9 @@
 >   tracking on the parent. Parent's `retry_count` stays as denormalised
 >   cache; service layer (`FormFailureRetryService`) keeps both in sync.
 >   `canBeRetried()` now correctly checks both `resolved_at` AND
->   `dismissed_at` (sessie 2 Q2 closure).
+>   `dismissed_at` (sessie 2 Q2 closure). Also adds `exception_trace`
+>   (longtext nullable) on `form_submission_action_failures` for the
+>   admin-UI triage view.
 >   RFC-WS-6.md §3 Q5 addendum.
 >
 > - v2.8: WS-6 session 3a.5 — `companies.kvk_number` column added
@@ -2593,6 +2595,7 @@ that aggregates the user's submitted, non-test `form_submissions`.
 | `failed_at`               | timestamp           |                                                                    |
 | `exception_class`         | string(255)         |                                                                    |
 | `exception_message`       | text                |                                                                    |
+| `exception_trace`         | longtext nullable   | Full PHP stack trace for triage (admin-UI). **v2.9 — WS-6 sessie 3c** |
 | `context`                 | json                | Free-form: `{target_entity, target_attribute, value_excerpt, merge_strategy}` |
 | `retry_count`             | tinyint unsigned    | default: 0                                                         |
 | `resolved_at`             | timestamp nullable  | Set when retry succeeds OR organiser marks resolved                |