Metro map interaction redesign: fit-to-view zoom, grid, branch handles, custom tracks

Phase 1 — Fit-to-view zoom:
- computeFitTransform() calculates bounding box and scales to fit all nodes
- Replaces hardcoded scale=1 reset in animateZoomReset() and initCanvas()
- Dim 1 no longer appears tiny after zooming out from dim 2

Phase 2 — Grid system:
- Shared gridConstants.js (GRID=50, GRID_STEP_X=200, GRID_STEP_Y=150)
- MapDataService snapToGrid() aligns all node positions server-side
- Canvas renders subtle grid lines (shown on interaction only, with fade)
- Line highlighting support via setHighlightedLine() for FAB hover

Phase 3 — Branch handles:
- Hover any station node → 3 "+" handles appear (0°/45°/315°)
- 0° extends the current line, 45°/315° fork to create new branch
- Ghost preview (dashed line + circle) on handle hover
- Handles only show at unoccupied grid positions
- Grid fades in during handle interaction, fades out after

Phase 4 — Custom tracks database:
- metro_lines table (project_id, naam, color, type, order)
- metro_nodes table (metro_line_id, naam, status, x, y, order)
- MetroLine + MetroNode models, controllers, routes
- Project.metroLines() relationship added

Phase 5+6 — FAB redesign + MetroMap wiring:
- FAB shows "Nieuw thema (lijn)" at root, "Nieuwe lijn" in project dim
- Track creation modal with retro-styled form
- MetroMap handles create-node events from branch handles
- Extend (0°) opens commitment/document form, fork opens track form
- Canvas context menu replaced with "hover to branch" hint

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

database/migrations/2026_04_08_000001_create_metro_lines_table.php

@@ -0,0 +1,26 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('metro_lines', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('project_id')->nullable()->constrained('projects')->cascadeOnDelete();
+            $table->string('naam', 255);
+            $table->string('color', 7);
+            $table->string('type');
+            $table->integer('order')->default(0);
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('metro_lines');
+    }
+};

database/migrations/2026_04_08_000002_create_metro_nodes_table.php

@@ -0,0 +1,29 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('metro_nodes', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('metro_line_id')->constrained('metro_lines')->cascadeOnDelete();
+            $table->string('naam', 255);
+            $table->text('beschrijving')->nullable();
+            $table->string('status')->default('active');
+            $table->integer('x')->default(0);
+            $table->integer('y')->default(0);
+            $table->integer('order')->default(0);
+            $table->foreignId('eigenaar_id')->nullable()->constrained('users')->nullOnDelete();
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('metro_nodes');
+    }
+};