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/static/sample.json

@@ -0,0 +1,138 @@
+{
+  "version": "1.0",
+  "event": {
+    "title": "Zimní výjezd oddílu",
+    "subtitle": "Víkendový zážitkový kurz pro mladé",
+    "date": "2026-03-01",
+    "location": "Chata Horní Lhota"
+  },
+  "program_types": [
+    {
+      "id": "morning",
+      "name": "Ranní program",
+      "color": "#F97316"
+    },
+    {
+      "id": "main",
+      "name": "Hlavní program",
+      "color": "#3B82F6"
+    },
+    {
+      "id": "rest",
+      "name": "Odpočinek",
+      "color": "#22C55E"
+    }
+  ],
+  "blocks": [
+    {
+      "id": "b1",
+      "date": "2026-03-01",
+      "start": "08:00",
+      "end": "08:30",
+      "title": "Budíček a rozcvička",
+      "type_id": "morning",
+      "responsible": "Kuba",
+      "notes": "Venkovní rozcvička, pokud počasí dovolí"
+    },
+    {
+      "id": "b2",
+      "date": "2026-03-01",
+      "start": "08:30",
+      "end": "09:00",
+      "title": "Snídaně",
+      "type_id": "rest",
+      "responsible": "Kuchyň",
+      "notes": null
+    },
+    {
+      "id": "b3",
+      "date": "2026-03-01",
+      "start": "09:00",
+      "end": "10:30",
+      "title": "Stopovací hra v lese",
+      "type_id": "main",
+      "responsible": "Lucka",
+      "notes": "Rozdělení do 4 skupin, mapky připraveny"
+    },
+    {
+      "id": "b4",
+      "date": "2026-03-01",
+      "start": "10:30",
+      "end": "11:00",
+      "title": "Svačina a pauza",
+      "type_id": "rest",
+      "responsible": null,
+      "notes": null
+    },
+    {
+      "id": "b5",
+      "date": "2026-03-01",
+      "start": "11:00",
+      "end": "12:30",
+      "title": "Stavba iglú / přístřešků",
+      "type_id": "main",
+      "responsible": "Petr",
+      "notes": "Soutěž o nejlepší stavbu, potřeba lopaty a plachty"
+    },
+    {
+      "id": "b6",
+      "date": "2026-03-01",
+      "start": "12:30",
+      "end": "14:00",
+      "title": "Oběd a polední klid",
+      "type_id": "rest",
+      "responsible": "Kuchyň",
+      "notes": "Guláš + čaj"
+    },
+    {
+      "id": "b7",
+      "date": "2026-03-01",
+      "start": "14:00",
+      "end": "16:00",
+      "title": "Orientační běh",
+      "type_id": "main",
+      "responsible": "Honza",
+      "notes": "Trasa 3 km, kontroly rozmístěny od rána"
+    },
+    {
+      "id": "b8",
+      "date": "2026-03-01",
+      "start": "16:00",
+      "end": "16:30",
+      "title": "Svačina",
+      "type_id": "rest",
+      "responsible": null,
+      "notes": null
+    },
+    {
+      "id": "b9",
+      "date": "2026-03-01",
+      "start": "16:30",
+      "end": "18:00",
+      "title": "Workshopy dle výběru",
+      "type_id": "morning",
+      "responsible": "Lucka + Petr",
+      "notes": "Uzlování / Orientace s buzolou / Kresba mapy"
+    },
+    {
+      "id": "b10",
+      "date": "2026-03-01",
+      "start": "18:00",
+      "end": "19:00",
+      "title": "Večeře",
+      "type_id": "rest",
+      "responsible": "Kuchyň",
+      "notes": null
+    },
+    {
+      "id": "b11",
+      "date": "2026-03-01",
+      "start": "19:00",
+      "end": "21:00",
+      "title": "Noční hra – Světlušky",
+      "type_id": "main",
+      "responsible": "Honza + Kuba",
+      "notes": "Potřeba: čelovky, reflexní pásky, vysílačky"
+    }
+  ]
+}