feat(timetable): API resources + LaneResolver helper

Six resources under app/Http/Resources/Api/V1/Artist/ matching
FormSubmissionResource conventions (final class, @mixin model,
optional()->toIso8601String, whenLoaded relationships).

  GenreResource          — id, name, color, sort_order, is_active
  ArtistResource         — master + lifetime/upcoming engagement counts
                           computed lazily from the engagements relation
  ArtistContactResource  — paired with ArtistResource.contacts
  ArtistEngagementResource — full deal block with the RFC D26 Buma/VAT
                           formulas computed live in `computed.*`:
                             buma_amount = fee × buma_pct/100
                                           IFF Organisation handles BUMA
                             vat_grondslag = fee + (buma when Organisation)
                             vat_amount = vat_grondslag × vat_pct/100
                                           when vat_applicable
                             total_cost = fee + buma + vat + Σ breakdown
                           Frontend (Session 5) ports the same formula.
  StageResource          — adds stage_days as a flat array of event_ids
                           (not nested Event resources, to keep payload
                           light)
  PerformanceResource    — `lane` (raw, persisted), `lane_resolved`
                           (computed per D19), `warnings` (overlap +
                           B2B at minimum; capacity-warn refined later)

LaneResolver under app/Services/Artist/ is the pure-logic helper that
PerformanceResource calls. Greedy lowest-non-conflicting lane
assignment over the (stage_id, event_id) cohort sorted by start_at
then by raw lane (so cascade-bumped rows stay where they were
visually). Frontend port lands in Session 4.

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

api/app/Http/Resources/Api/V1/Artist/PerformanceResource.php

@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Resources\Api\V1\Artist;
+
+use App\Models\Performance;
+use App\Services\Artist\LaneResolver;
+use Carbon\CarbonImmutable;
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+/**
+ * @mixin Performance
+ */
+final class PerformanceResource extends JsonResource
+{
+    /**
+     * @return array<string, mixed>
+     */
+    public function toArray(Request $request): array
+    {
+        return [
+            'id' => $this->id,
+            'engagement_id' => $this->engagement_id,
+            'event_id' => $this->event_id,
+            'stage_id' => $this->stage_id,
+            'lane' => (int) $this->lane,
+            'lane_resolved' => $this->resolveLane(),
+            'start_at' => optional($this->start_at)->toIso8601String(),
+            'end_at' => optional($this->end_at)->toIso8601String(),
+            'version' => (int) $this->version,
+            'notes' => $this->notes,
+            'warnings' => $this->computeWarnings(),
+            'engagement' => ArtistEngagementResource::make($this->whenLoaded('engagement')),
+            'stage' => StageResource::make($this->whenLoaded('stage')),
+            'created_at' => optional($this->created_at)->toIso8601String(),
+            'updated_at' => optional($this->updated_at)->toIso8601String(),
+            'deleted_at' => optional($this->deleted_at)->toIso8601String(),
+        ];
+    }
+
+    /**
+     * Computed via LaneResolver over the (stage, sub-event) cohort.
+     * For parked performances (stage_id = null) the persisted lane is
+     * surfaced as-is — the wachtrij is a flat list, not a lane grid.
+     */
+    private function resolveLane(): int
+    {
+        if ($this->stage_id === null) {
+            return (int) $this->lane;
+        }
+
+        $cohort = Performance::query()
+            ->where('stage_id', $this->stage_id)
+            ->where('event_id', $this->event_id)
+            ->get();
+
+        $resolved = app(LaneResolver::class)->resolve($cohort);
+
+        return $resolved[(string) $this->id] ?? (int) $this->lane;
+    }
+
+    /**
+     * RFC v0.2 D5 / D6 / D25 — overlap, B2B, capacity warnings.
+     * Naive implementation for Session 2; refined as the timetable
+     * frontend lands in Session 4.
+     *
+     * @return array<int, string>
+     */
+    private function computeWarnings(): array
+    {
+        $warnings = [];
+
+        if ($this->stage_id === null) {
+            return $warnings;
+        }
+
+        $start = CarbonImmutable::instance($this->start_at);
+        $end = CarbonImmutable::instance($this->end_at);
+
+        $peers = Performance::query()
+            ->where('stage_id', $this->stage_id)
+            ->where('event_id', $this->event_id)
+            ->where('id', '!=', $this->id)
+            ->get();
+
+        foreach ($peers as $other) {
+            $oStart = CarbonImmutable::instance($other->start_at);
+            $oEnd = CarbonImmutable::instance($other->end_at);
+
+            if ($start < $oEnd && $oStart < $end && (int) $other->lane === (int) $this->lane) {
+                $warnings[] = 'overlap';
+                break;
+            }
+        }
+
+        foreach ($peers as $other) {
+            $oEnd = CarbonImmutable::instance($other->end_at);
+            $oStart = CarbonImmutable::instance($other->start_at);
+            if ($oEnd->equalTo($start) || $oStart->equalTo($end)) {
+                $warnings[] = 'b2b';
+                break;
+            }
+        }
+
+        return array_values(array_unique($warnings));
+    }
+}