Add the map-table vision pipeline

Reads a screenshot of the in-game map table and recovers where on the board
it is looking. The scene is a flat table under a perspective camera, so a
single homography describes grid<->screen exactly; that is fitted from line
evidence (LSD segments, vanishing-point RANSAC, 1-D lattice fits).

Line evidence alone cannot finish the job: the 1km cells and the 100m
subgrid are locally identical, so it fixes neither scale, axis assignment,
axis direction nor phase. Those come from the cell labels -- and the labels
are never *detected*, they are correlated where the grid says they must be
(9% in from a cell's left edge, 6% down from its top). Blob detection on
aerial-photo terrain finds texture, not glyphs; correlating a known template
at a known place has no such failure mode. The same score then ranks the
geometry hypotheses, since a wrong lattice puts the crop where no label is,
so one number resolves scale, axis assignment, direction, phase and anchor
together.

Markers are found by hostile/friendly colour plus an IoU test against an
ideal inscribed diamond, which cut a red-lit shot from 43 false positives to
2 while preserving every hand-verified count. Unit-type classification is
present but not yet reliable, and returns unknown rather than guessing.

Measured over the fixture set: 7 of 10 solve, each with 100% of its
ground-truth points in the correct cell (85/112 overall), residual spread
0.005-0.033 cells. The other three reject cleanly; none has ever produced a
plausible-but-wrong grid. Across 122 typewriter screenshots solve() accepted
none, which is what makes clipboard routing safe.

Fixtures: 10 map shots with hand-transcribed ground truth, plus 10
typewriter shots spanning 262-5366px for routing and future OCR tests. Map
shots wider than 2400px (the pipeline's own maximum working width) were
downscaled with their coordinates rescaled to match; re-measured afterwards,
the results are identical. Typewriter shots stay at native resolution
because OCR needs the text legible.

Drops docs/map_vision_plan.md and its WIP prototype: the design now lives in
the module docstring, next to the code it describes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/fixtures/map_shots/too_hard/README.md

@@ -0,0 +1,14 @@
+# Screenshots we deliberately do not try to solve
+
+Kept for the record, excluded from the evaluation set. These fail for reasons
+that are properties of the screenshot, not of the algorithm, so working around
+them would mean guessing:
+
+- `06.png`, `14.png` — exactly ONE grid label visible. A single label cannot be
+  cross-checked, so a misread would silently shift the whole board with nothing
+  to contradict it. Two mutually consistent labels is the minimum safe anchor.
+- `12.png` — 710x594 native. Too few pixels per cell for the label glyphs to
+  correlate; measured, the best label score stays ~0.44 at every working
+  resolution, so it is not a tuning problem.
+
+"Too zoomed in" and "too low resolution" are legitimate hard rejections.