Fix clipped receipt margins, add time-of-day naming, speed up rotation detection

- vision/document.py: pad_quad() expands the detected quad outward
  before warping so a straight-line contour fit doesn't clip the first
  character of every line on a slightly curled/wrinkled receipt
- ocr/extract.py + llm/vision.py: extract transaction time (HH:MM) so
  same-day repeat visits to a vendor get distinct filenames
  (2023-03-20_1525_walmart.pdf vs. a later same-day trip)
- vision/orient.py: downscale before Tesseract OSD/confidence-sweep
  rotation detection — this was the dominant cost in the detection
  phase (7x speedup: 472s -> 67s on a 36s test video)

config.yaml

@@ -47,6 +47,11 @@ document:
   enhance: false
   # Auto-detect and correct 0/90/180/270 rotation before OCR/PDF export.
   auto_rotate: true
+  # Expand the detected quad outward by this fraction before warping, to
+  # recover paper margins clipped by curl/wrinkles (straight-line quad vs.
+  # a slightly bowed real edge). refine.tighten below trims any extra
+  # mat/background this pulls in back off.
+  pad_margin: 0.04
   # Tighten crops to the actual paper region (cuts mat margins/hands) and
   # inpaint fingers pressing on the page.
   refine: true