feat(api): add tags to resource creation

Normalize tag names before attaching them, reject names that are too short
after sanitization, and return 404 when removing tags not attached to the
resource.

Adds a per-team unique tag-name index and migrates duplicate tags onto the
kept record before creating the constraint.

database/migrations/2026_07_07_113248_add_team_name_unique_index_to_tags_table.php

@@ -0,0 +1,76 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        if ($this->indexExists()) {
+            return;
+        }
+
+        DB::table('tags')
+            ->select('team_id', 'name', DB::raw('MIN(id) as keep_id'), DB::raw('COUNT(*) as tag_count'))
+            ->whereNotNull('team_id')
+            ->groupBy('team_id', 'name')
+            ->havingRaw('COUNT(*) > 1')
+            ->orderBy('keep_id')
+            ->cursor()
+            ->each(function ($duplicate): void {
+                DB::table('tags')
+                    ->select('id')
+                    ->where('team_id', $duplicate->team_id)
+                    ->where('name', $duplicate->name)
+                    ->where('id', '!=', $duplicate->keep_id)
+                    ->orderBy('id')
+                    ->cursor()
+                    ->each(function ($duplicateTag) use ($duplicate): void {
+                        DB::table('taggables')
+                            ->where('tag_id', $duplicateTag->id)
+                            ->orderBy('taggable_id')
+                            ->cursor()
+                            ->each(function ($taggable) use ($duplicate): void {
+                                DB::table('taggables')->updateOrInsert([
+                                    'tag_id' => $duplicate->keep_id,
+                                    'taggable_id' => $taggable->taggable_id,
+                                    'taggable_type' => $taggable->taggable_type,
+                                ]);
+                            });
+
+                        DB::table('taggables')->where('tag_id', $duplicateTag->id)->delete();
+                        DB::table('tags')->where('id', $duplicateTag->id)->delete();
+                    });
+            });
+
+        Schema::table('tags', function (Blueprint $table) {
+            $table->unique(['team_id', 'name'], 'tags_team_id_name_unique');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        if (! $this->indexExists()) {
+            return;
+        }
+
+        Schema::table('tags', function (Blueprint $table) {
+            $table->dropUnique('tags_team_id_name_unique');
+        });
+    }
+
+    private function indexExists(): bool
+    {
+        return collect(Schema::getIndexes('tags'))
+            ->contains(fn (array $index): bool => $index['name'] === 'tags_team_id_name_unique');
+    }
+};