Add Hough line / grid / separator detection

[JE-Chen]

grid_locator clusters already-found boxes and shape_locator finds closed rectangles — neither finds a table's ruling lines or a UI divider from raw pixels.

• find_lines (AC_find_lines): Canny + probabilistic Hough segments as {x1,y1,x2,y2,angle,length,orientation} (horizontal/vertical/diagonal), longest first, with an orientation filter.
• find_grid (AC_find_grid): clusters horizontal rules → rows, vertical rules → cols, returns {rows, cols, cells} so you can address "row 3, col 2".
• find_separators (AC_find_separators): merged coordinates of long divider lines along an axis.
• Reuses visual_match._haystack_gray (no copied loader); injectable haystack → headless-testable on a synthetic 3×3 grid (blank → no lines). Base OpenCV (cv2.HoughLinesP), lazy imports. Wired through all 5 layers + headless test + EN/Zh docs + WHATS_NEW. Qt-free.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codacy-production]

Not up to standards ⛔

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