refactor: migrar reportes a Typst con plantilla compartida y scripts

- Reemplazar plantillas Markdown por template/report.typ y template/main.typ
- Agregar primer reporte: respuesta-observaciones-avance-1
- Agregar scripts build.sh, preview.sh y common.sh con salida en pdf/
- Actualizar README y AGENTS.md; simplificar .gitignore

scripts/preview.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+source "$(dirname -- "${BASH_SOURCE[0]}")/common.sh"
+if [[ "$force" == true ]]; then
+  require_typst
+  mkdir -p -- "$repo_root/pdf"
+  exec typst watch --root "$repo_root" "$input" "$output" --open
+fi
+build_pdf
+# Use an absolute path so the viewer also handles names starting with a dash.
+pdf_path="$(cd -- "$(dirname -- "$output")" && pwd)/$(basename -- "$output")"
+if command -v xdg-open >/dev/null 2>&1; then
+  exec xdg-open "$pdf_path"
+elif command -v open >/dev/null 2>&1; then
+  exec open "$pdf_path"
+else
+  echo "Error: no PDF opener found (xdg-open or open). PDF: $pdf_path" >&2
+  exit 1
+fi