feat: přidáno URL pole pro bloky – klikatelný odkaz v PDF

- Block model: nové volitelné pole 'url' (Optional[str])
- Frontend: URL input v modálu pro přidání/editaci bloku
- PDF generátor: c.linkURL() – celý blok je klikatelný odkaz
- sample.json: ukázkový blok s URL
- index.html: dokumentace URL pole
- .github/copilot-instructions.md: přidány Copilot instrukce

.github/copilot-instructions.md

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+# Copilot instructions for scenar-creator
+
+## Big picture (read this first)
+- This is a single FastAPI service that serves both API and static frontend (no separate frontend build step).
+- Entry point: `app/main.py` mounts `/static` and serves `index.html` at `/`.
+- API boundary is under `app/api/` (`/api/health`, `/api/validate`, `/api/sample`, `/api/generate-pdf`).
+- Core domain object is `ScenarioDocument` in `app/models/event.py` (JSON-first design, no DB).
+- PDF rendering is the main backend logic in `app/core/pdf_generator.py` (ReportLab canvas, A4 landscape timetable).
+
+## Data model and domain rules (project-specific)
+- Multi-day events use `event.date_from` + `event.date_to`; keep backward compatibility with legacy `event.date`.
+- `blocks[].date` is always a concrete day (`YYYY-MM-DD`) even for multi-day events.
+- Overnight blocks are valid: `end <= start` means crossing midnight. This rule exists in frontend canvas and backend PDF.
+- `series_id` groups blocks created by “add to all days”; deleting a series removes all blocks with matching `series_id`.
+- `program_types[].id` must match each `blocks[].type_id`; unknown types are validation errors.
+
+## Frontend architecture conventions
+- Frontend is vanilla JS globals loaded in order from `index.html`: `API` -> `Canvas` -> import/export helpers -> `App`.
+- `App.state` is the source of truth (`event`, `program_types`, `blocks`) in `app/static/js/app.js`.
+- Canvas timeline is horizontal time axis with 15-minute snapping (`Canvas.GRID_MINUTES = 15`) in `app/static/js/canvas.js`.
+- Drag/resize behavior: native pointer drag for move + interact.js resize handle for duration updates.
+- UI copy and date labels are Czech (e.g., `Pondělí (20.2)`), so preserve localization in new UI text.
+
+## Backend conventions
+- Keep API handlers thin; place formatting/rendering logic in `app/core/`.
+- Raise `ScenarsError` from core logic and translate to HTTP 422 in API (`app/api/pdf.py`).
+- PDF generator handles:
+  - legend from `program_types`
+  - optional responsible person text inside blocks
+  - notes as superscript markers + optional page 2 note listing
+- Czech diacritics in PDFs rely on LiberationSans registration with Helvetica fallback.
+
+## Developer workflows
+- Local run: `uvicorn app.main:app --reload --port 8080`
+- Tests: `python3 -m pytest tests/ -v`
+- Container image includes required fonts (`fonts-liberation`) in `Dockerfile`; do not remove unless PDF text rendering is reworked.
+- Health endpoint for local/container checks: `/api/health`.
+
+## Testing patterns to preserve
+- API tests use `fastapi.testclient.TestClient` (`tests/test_api.py`).
+- PDF tests assert magic header `%PDF-` and page count with regex (`tests/test_pdf.py`).
+- Keep coverage for overnight blocks, multi-day ranges, legacy `event.date`, and `series_id` behavior when changing models/UI.
+
+## High-impact files
+- `app/core/pdf_generator.py` — timeline layout math, fonts, notes page logic.
+- `app/static/js/canvas.js` — drag/resize + time-range computation.
+- `app/static/js/app.js` — modal save/delete logic, series expansion, document import/export shape.
+- `app/models/event.py` — schema contract used by both API and frontend JSON.