Implements Phase 6 tasks 1-4: Task 1: Add physicalLayout() to layout.ts - Exports new physical layout function with tighter spacing - Uses dagre top-to-bottom layout for PE cluster visualization Task 2: Add PE cluster, cross-PE, and intra-PE styles to style.ts - PE cluster parent nodes: rounded rectangle with solid border - Cross-PE edges: thicker, darker (3px, #5c6bc0) - Intra-PE edges: lighter (1.5px, #bbb) Task 3: Add view toggle and physical element building to main.ts - buildPhysicalLabel(): formats nodes with [iram:offset, ctx:slot] annotations - buildPhysicalElements(): creates PE cluster nodes and assigns children - View mode tracking: logical (default) or physical - Toggle button in index.html switches between views - Physical view only available when stage == 'allocate' - Disables toggle and reverts to logical if graph becomes incomplete Task 4: Manual verification - esbuild bundle succeeds without errors (1.2mb) - Full test suite passes: 608/608 tests - Frontend builds successfully with npm run build Acceptance criteria covered: - AC3.1: Nodes grouped into PE cluster boxes by PE ID - AC3.2: Nodes annotated with IRAM offset and context slot - AC3.3: Cross-PE edges visually distinct from intra-PE - AC3.4: Physical view unavailable when stage != 'allocate'