feat(papers): estructura, scaffolding y capability page del artefacto papers/

Nuevo tipo de artefacto para papers académicos reproducibles (papers/<NNNN-slug>/):

- Plantillas docs/templates/paper.md (IMRaD completo con guías por sección:
  Abstract, Introduction, Related work, Methods, Results, Discussion con
  Limitaciones + Amenazas a la validez, Conclusion + Future work) y
  docs/templates/preregistration.md (H0/H1 falsable, variables, diseño, plan
  de análisis con test exacto + effect size + corrección múltiple, predicción
  cuantitativa; nota anti-HARKing de congelado).
- Pipeline init_paper (bash/functions/pipelines/init_paper.sh + .md): calcula el
  siguiente NNNN, crea las subcarpetas (experiments data figures reviews out),
  copia las plantillas rellenando el frontmatter (title, slug, date, phase=question,
  status=draft) y crea references.md. No hace git init (fase interna local).
- Función atómica reutilizable next_numbered_dir (bash/functions/io): siguiente
  prefijo NNNN- escaneando un directorio numerado (reutilizable por papers/reports/issues).
- papers/ como artefacto local gitignored (bloque en .gitignore + papers/.gitkeep):
  un paper en fase interna no contamina el repo padre; al promocionar a publishable
  se vuelve sub-repo Gitea propio.
- Página de capacidad docs/capabilities/papers.md + fila en el INDEX: tabla de
  funciones del grupo papers (disponibles + en construcción por la flota), ejemplo
  canónico end-to-end y fronteras.

Reutiliza slugify_ascii del registry. Diseño: reports/0001-2026-06-30-papers-system-design.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bash/functions/io/next_numbered_dir.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# next_numbered_dir — Compute the next NNNN- prefix for a numbered directory.
+#
+# Scans the DIRECT subdirectories of <parent_dir> whose names start with a
+# numeric prefix of the form `NNNN-` (4+ digits followed by a hyphen), takes
+# the maximum number, adds 1, and prints it zero-padded to <width> (default 4).
+# If <parent_dir> does not exist or contains no matching subdir, prints the
+# first number (0001 at default width).
+
+next_numbered_dir() {
+    local parent_dir="${1:-}"
+    local width="${2:-4}"
+
+    if [[ -z "$parent_dir" ]]; then
+        echo "usage: next_numbered_dir <parent_dir> [width]" >&2
+        return 1
+    fi
+
+    local max=0
+    local entry base num
+
+    if [[ -d "$parent_dir" ]]; then
+        # Iterate only over direct subdirectories. The trailing slash in the
+        # glob ensures files (e.g. .gitkeep) are skipped — only dirs match.
+        for entry in "$parent_dir"/*/; do
+            # If the glob matched nothing it stays literal; guard with -d.
+            [[ -d "$entry" ]] || continue
+            base="$(basename "$entry")"
+            # Require a prefix of 4+ digits followed by a hyphen.
+            if [[ "$base" =~ ^([0-9]{4,})- ]]; then
+                num="${BASH_REMATCH[1]}"
+                # Force base 10 so leading zeros (08, 09) are not read as octal.
+                num=$((10#$num))
+                if (( num > max )); then
+                    max=$num
+                fi
+            fi
+        done
+    fi
+
+    printf "%0*d\n" "$width" $(( max + 1 ))
+}
+
+if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
+    next_numbered_dir "$@"
+fi