feat: v3.0 - canvas editor, JSON-only, no Excel, new UI

- Remove all Excel code (import, export, template, pandas, openpyxl)
- New canvas-based schedule editor with drag & drop (interact.js)
- Modern 3-panel UI: sidebar, canvas, documentation tab
- New data model: Block with id/date/start/end, ProgramType with id/name/color
- Clean API: GET /api/health, POST /api/validate, GET /api/sample, POST /api/generate-pdf
- Rewritten PDF generator using ScenarioDocument directly (no DataFrame)
- Professional PDF output: dark header, colored blocks, merged cells, legend, footer
- Sample JSON: "Zimní výjezd oddílu" with 11 blocks, 3 program types
- 30 tests passing (API, core models, PDF generation)

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

app/models/responses.py

@@ -1,6 +1,6 @@
 """API response models."""
 
-from typing import Any, List, Optional
+from typing import List
 
 from pydantic import BaseModel
 
@@ -13,10 +13,3 @@ class HealthResponse(BaseModel):
 class ValidationResponse(BaseModel):
     valid: bool
     errors: List[str] = []
-
-
-class ImportExcelResponse(BaseModel):
-    success: bool
-    document: Optional[Any] = None
-    errors: List[str] = []
-    warnings: List[str] = []