feat(pdf): tool page with Extract / Build / Manage modes

Phase 3/6. Wires the PDF Extractor into the GUI as a new
"transformations" tool with three modes selected by a horizontal
radio at the top of the page:

**Extract** — pick a saved template, upload one or more
statement PDFs (single + batch shipping together to keep the
common case one-step), get a previewed DataFrame + CSV download.
Per-file row counts and warnings are surfaced; failures on one
file don't kill the whole batch. The combined CSV gets a
``source_file`` first column so the accountant can sort/filter
by statement.

**Build template** — load an existing template or start fresh,
upload a sample PDF, edit every schema field across four tabs
(Pages & table / Columns / Parsing / Save). A live preview below
re-runs ``apply_template`` against the sample on each re-render
so the user sees their changes hit rows immediately. The column-
boundary editor is text-input ("comma-separated x-positions") for
now — replaced by the drawable-canvas visual picker in commit 5.

**Manage templates** — list with rename / delete / export
(downloads the canonical JSON) / import (uploads someone else's
JSON, validated through ``template_from_json``).

Heavy work (``extract_pages_auto``) only runs on explicit user
action (Extract / a new sample upload), and the parsed Page list
is cached in ``st.session_state`` so widget-edit reruns don't
re-parse the PDF.

Logging: tool runs and template saves both hit the audit log via
``log_event("tool_run", …)``, matching every other tool's
instrumentation pattern.

Registered in ``tools_registry.py`` under ``transformations``
with status ``Ready`` and the picture-as-pdf Material icon. i18n
keys added for en + es ("PDF to CSV" / "PDF a CSV").

OCR is wired in this commit — ``extract_pages_auto`` already
falls back through ``pytesseract`` when the binary is available,
and the warning strings it returns surface as ``st.info`` /
``st.warning`` per-file. Commit 6 will polish the OCR UX with a
status row.

Next commits build on this page:
  4 — batch progress + cancellation + per-file error grouping
  5 — drawable-canvas visual picker replaces text x-positions
  6 — OCR availability banner + scanned-page indicators

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/i18n/packs/es.json

@@ -158,6 +158,12 @@
       "description": "Encadena herramientas en el orden recomendado y pasa la salida entre pasos.",
       "page_title": "Flujos automatizados",
       "page_caption": "Encadena pasos de limpieza de DataTools en un flujo repetible. La canalización recomienda un orden; tú mantienes el control."
+    },
+    "10_pdf_extractor": {
+      "name": "PDF a CSV",
+      "description": "Extrae transacciones de extractos bancarios en PDF usando plantillas reutilizables por origen.",
+      "page_title": "PDF a CSV",
+      "page_caption": "Extrae tablas de transacciones de extractos bancarios en PDF. Crea una plantilla por origen y reutilízala para cada extracto que siga el mismo formato. Se ejecuta localmente — tus datos no salen de este equipo."
     }
   },
   "nav": {