feat: Add Kits + FurnaceSplitter plugin config modules

DB migrations 016 (kits_configs) and 019 (furnacesplitter_configs) applied.
Backend: NestJS modules with CRUD, apply-to-server, import-from-server.
Frontend: Pinia stores, Vue views with config editor, router + nav wiring.
Kits view: 3-tab editor (list/editor/settings), kit items with shortname/amount/skinId/container.
FurnaceSplitter view: per-furnace toggles, split count, fuel multiplier settings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/migrations/016_kits_configs.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS kits_configs (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    license_id UUID NOT NULL REFERENCES licenses(id) ON DELETE CASCADE,
+    config_name VARCHAR(100) NOT NULL,
+    description TEXT,
+    config_data JSONB NOT NULL DEFAULT '{}',
+    is_active BOOLEAN NOT NULL DEFAULT false,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_kits_configs_license ON kits_configs(license_id);

backend/migrations/019_furnacesplitter_configs.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS furnacesplitter_configs (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    license_id UUID NOT NULL REFERENCES licenses(id) ON DELETE CASCADE,
+    config_name VARCHAR(100) NOT NULL,
+    description TEXT,
+    config_data JSONB NOT NULL DEFAULT '{}',
+    is_active BOOLEAN NOT NULL DEFAULT false,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_furnacesplitter_configs_license ON furnacesplitter_configs(license_id);