refactor: complete migration to template-v2 architecture

- Remove legacy template.svg files from example/ and my-project/
- Simplify generator.js by removing generateHardcoded method (326→210 lines, -36%)
- Add strict template validation with clear error messages
- Remove all fallback mechanisms - template-v2.svg format now required
- Clean up tests: remove hardcoded generation tests, keep template-based tests
- Add comprehensive e2e tests (large datasets, edge cases, error handling)
- Update documentation: mark REFACTORING_PLAN.md complete, add TEMPLATE_V2_GUIDE.md
- All 56 tests passing (16 engine + 25 generator + 15 integration)

BREAKING CHANGE: Old template.svg format no longer supported. Must use template-v2.svg with <g id="*-template"> elements in defs section.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

test/testHelpers.js

@@ -43,12 +43,100 @@ T-1,First Task,Development,2025-01-15
 T-2,Second Task,Testing,2025-02-20
 T-3,Third Task,Development,2025-03-10`
 
+// Create a proper template-v2.svg format with template elements in defs
 export const createSampleTemplate = () => `<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <!-- Month template -->
+    <g id="month-template" style="display:none">
+      <line x1="{{MONTH_X}}" y1="{{GRID_TOP}}" x2="{{MONTH_X}}" y2="{{GRID_BOTTOM}}" stroke="#E0E0E0" stroke-width="1"/>
+      <rect x="{{MONTH_X_OFFSET}}" y="{{MONTH_LABEL_Y_OFFSET}}" width="60" height="24" fill="#F5F5F5" rx="4"/>
+      <text x="{{MONTH_TEXT_X}}" y="{{MONTH_LABEL_Y}}" font-family="Arial" font-size="12" fill="#424242">{{MONTH_LABEL}}</text>
+      <line x1="{{MONTH_SEP_X}}" y1="{{GRID_TOP}}" x2="{{MONTH_SEP_X}}" y2="{{GRID_BOTTOM}}" stroke="#BDBDBD" stroke-width="2"/>
+    </g>
+
+    <!-- Lane template -->
+    <g id="lane-template" style="display:none">
+      <rect x="{{LANE_X}}" y="{{LANE_Y}}" width="{{LANE_WIDTH}}" height="{{LANE_HEIGHT}}" fill="#FAFAFA" stroke="#E0E0E0" rx="8"/>
+      <text x="{{LABEL_X}}" y="{{LABEL_Y}}" font-family="Arial" font-size="14" font-weight="bold" fill="#212121">{{LANE_NAME}}</text>
+    </g>
+
+    <!-- Task template -->
+    <g id="task-template" style="display:none">
+      <circle cx="{{TASK_X}}" cy="{{TASK_Y}}" r="6" fill="#1976D2"/>
+      <text x="{{TEXT_X}}" y="{{TEXT_Y}}" font-family="Arial" font-size="11" fill="#424242">{{TASK_ID}} {{TASK_TITLE}}</text>
+    </g>
+  </defs>
+
   <rect width="100%" height="100%" fill="#FFFFFF"/>
   {{MONTHS}}
   {{LANES}}
 </svg>`
 
+// Create a malformed template missing required elements (for error testing)
+export const createMalformedTemplate = (missingElement = 'month-template') => {
+  const templates = {
+    'month-template': `<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <g id="lane-template" style="display:none">
+      <rect x="{{LANE_X}}" y="{{LANE_Y}}" width="{{LANE_WIDTH}}" height="{{LANE_HEIGHT}}" fill="#FAFAFA"/>
+    </g>
+    <g id="task-template" style="display:none">
+      <circle cx="{{TASK_X}}" cy="{{TASK_Y}}" r="6" fill="#1976D2"/>
+    </g>
+  </defs>
+  {{MONTHS}}
+  {{LANES}}
+</svg>`,
+    'lane-template': `<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <g id="month-template" style="display:none">
+      <line x1="{{MONTH_X}}" y1="{{GRID_TOP}}" x2="{{MONTH_X}}" y2="{{GRID_BOTTOM}}" stroke="#E0E0E0"/>
+    </g>
+    <g id="task-template" style="display:none">
+      <circle cx="{{TASK_X}}" cy="{{TASK_Y}}" r="6" fill="#1976D2"/>
+    </g>
+  </defs>
+  {{MONTHS}}
+  {{LANES}}
+</svg>`,
+    'task-template': `<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <g id="month-template" style="display:none">
+      <line x1="{{MONTH_X}}" y1="{{GRID_TOP}}" x2="{{MONTH_X}}" y2="{{GRID_BOTTOM}}" stroke="#E0E0E0"/>
+    </g>
+    <g id="lane-template" style="display:none">
+      <rect x="{{LANE_X}}" y="{{LANE_Y}}" width="{{LANE_WIDTH}}" height="{{LANE_HEIGHT}}" fill="#FAFAFA"/>
+    </g>
+  </defs>
+  {{MONTHS}}
+  {{LANES}}
+</svg>`
+  }
+  return templates[missingElement] || templates['month-template']
+}
+
+// Create a large dataset for stress testing (50+ items)
+export const createLargeDataset = (itemCount = 60) => {
+  const lanes = ['Development', 'Testing', 'Design', 'DevOps', 'Documentation']
+  const startDate = new Date('2025-01-01')
+  const items = []
+
+  for (let i = 1; i <= itemCount; i++) {
+    const daysOffset = Math.floor(i * 8) // Spread items across ~480 days (16 months)
+    const dueDate = new Date(startDate)
+    dueDate.setDate(dueDate.getDate() + daysOffset)
+
+    items.push({
+      id: `TASK-${i}`,
+      title: `Task ${i}: Implementation Item`,
+      lane: lanes[i % lanes.length],
+      due: dueDate
+    })
+  }
+
+  return items
+}
+
 export const mockFetch = (data, ok = true) => {
   global.fetch.mockResolvedValueOnce({
     ok,