feat: find shared ground across map slugs, and let every map say its origin

Two sources need not divide a world the same way: IGN draws Iki Island
as a map of its own, and MapGenie draws it inside the Tsushima sheet.
A shared slug was the only evidence of shared ground the composition
accepted, so the same places arrived twice, projected differently, and
no coordinate could say so. The places themselves can: before a map
joins a game as new ground, it is tried against every map the game
already draws, and an affine that closes on their shared names is the
proof of overlap no geohash could give. Iki Island's fit closes on 52
names at a median of two pixels -- the wiki's data is the same survey
-- so its pins resolve into the sheet, one Crimson Dye Merchant where
there were two, and its raster lands as an aligned variant of the
sheet. The warp planner pairs captures the same way now, by fit rather
than by slug.

And provenance is part of the map, not a side effect of merging: every
map opens its account with an origin entry naming the source it came
from, single-source games included, so the card and the workbench can
answer for every pin -- the origin's own, the origin corroborated, or
a donor's contribution. The policy revision rises to 3 and the library
repackages under it.

commit

cb57f1120adb0b58f5accf7dee7e0eb2fa7ea966

parent

73127bacd89d679c375fa608017e8015b7ced84c

author

Dami <dami.etoile@gmail.com>