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/common.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Shared setup; sourced by build.sh and preview.sh.
+set -euo pipefail
+repo_root="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
+usage() {
+  echo "Usage: $0 [--force|-f] [document.typ | report-directory]"
+  echo "Defaults to reports/respuesta-observaciones-avance-1/main.typ. Relative paths use the current directory."
+  echo "Existing PDFs are preserved unless --force is given. Preview watches only with --force."
+}
+force=false
+input=""
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --force|-f) force=true ;;
+    --help|-h) usage; exit 0 ;;
+    -*) echo "Error: unknown option: $1" >&2; usage >&2; exit 2 ;;
+    *)
+      if [[ -n "$input" ]]; then usage >&2; exit 2; fi
+      input="$1"
+      ;;
+  esac
+  shift
+done
+input="${input:-$repo_root/reports/respuesta-observaciones-avance-1/main.typ}"
+if [[ -d "$input" ]]; then input="$input/main.typ"; fi
+if [[ ! -f "$input" || "$input" != *.typ ]]; then
+  echo "Error: expected an existing .typ file: $input" >&2
+  exit 1
+fi
+input="$(realpath -- "$input")"
+case "$input" in
+  "$repo_root/template/"*)
+    echo "Error: las plantillas no generan PDF; copie el documento base a reports/ primero." >&2
+    exit 1
+    ;;
+esac
+name="$(basename -- "$input" .typ)"
+if [[ "$name" == main ]]; then
+  name="$(basename -- "$(cd -- "$(dirname -- "$input")" && pwd)")"
+fi
+output="$repo_root/pdf/$name.pdf"
+
+require_typst() {
+  command -v typst >/dev/null 2>&1 || {
+    echo "Error: install Typst and make it available on PATH." >&2
+    exit 1
+  }
+}
+
+build_pdf() {
+  if [[ -e "$output" && "$force" == false ]]; then
+    printf 'PDF existente: %s (use --force para regenerar)\n' "$output"
+    return
+  fi
+  require_typst
+  mkdir -p -- "$repo_root/pdf"
+  typst compile --root "$repo_root" "$input" "$output"
+  printf 'PDF: %s\n' "$output"
+}