feat: text-layer grounding (extractor authority, guard rescue tier, verifier oracle + hi-DPI crops)

- backend/text_layer.py: PyMuPDF text-layer extraction, fuzzy evidence
  bbox matching, 300-DPI crop rendering, coverage-gap signal
- extractor (classic + agent): TEXT LAYER block appended at call sites;
  grounding guard gains text-layer rescue tier (grounding=text_layer stamp)
- verifier: {text_layer} oracle excerpt + evidence-located hi-DPI crops
  replacing full-page images (fallback preserved, I2 guard intact)
- coverage gaps: text-bearing pages with zero extraction -> failed-scope
  gap findings (agent) / log-only (classic)
- config knobs: TEXT_LAYER_ENABLED/MIN_CHARS/MAX_CHARS, VERIFY_TEXT_MAX_CHARS,
  VERIFY_HI_DPI_CROPS, VERIFY_CROP_DPI, VERIFY_CROP_MARGIN_PTS
- tests: 22 new (text_layer unit, grounding/render, runner-level flow)
Spec: docs/superpowers/specs/2026-08-12-text-layer-grounding-design.md

backend/pipeline/runner.py

@@ -27,6 +27,7 @@ from typing import Dict, Optional, Callable
 
 from backend.pipeline.pdf_processor import convert_pdf_to_images
 from backend.pipeline.extractor import extract_assertions
+from backend.text_layer import attach_text_layers, coverage_gaps
 from backend.pipeline.sheet_index import classify_sheets, derive_project_meta_from_cover
 from backend.pipeline.jurisdiction import run_jurisdiction
 from backend.pipeline.normalizer import normalize_assertions, build_project_intelligence
@@ -103,9 +104,12 @@ def _run_stages(
 ) -> Dict:
     stage("PDF -> images")
     pages = convert_pdf_to_images(pdf_path)
+    text_dir = os.path.join(out_dir, "text") if out_dir else None
+    attach_text_layers(pdf_path, pages, text_dir=text_dir)
 
     stage("Extract assertions")
     sheets = extract_assertions(pages)
+    coverage_gaps(pages, sheets)  # classic: log-only recall signal
 
     stage("Classify sheet index")
     sheet_index = classify_sheets(sheets)