refactor(maps): remove redundant filename-derived tiling metadata

[zoeyrose]

Summary

Now that Classic restores filename-derived map tiling, remove redundant
manually authored tile_path_N records from content@main wherever the
canonical coordinate filename already identifies the same existing neighbor.
Remove the paired celestial_boundary_N record when the link is intentionally
runtime-derived and has no authored seam-policy exception.

The horizontal runtime/static behavior is covered by
atrinik/classic#526 and
atrinik/content#260. The
vertical contract needed to remove tile_path_9/tile_path_10 is tracked in
atrinik/classic#530.

Current inventory

An audit of the current main source (08e8bc869) found:

• 3,660 authored map files;
• 3,515 files containing 25,010 tile_path_N records, each paired with a
  celestial_boundary_N record;
• 22,784 records whose targets exactly match an existing neighbor derived from
  the current ten-slot coordinate-filename rules, including 21,940 horizontal
  records and 844 vertical records; and
• 356 files / 2,226 records whose names are not parsed by the current
  coordinate convention, including the four-digit planes/creation layout and
  legacy-named shattered_islands maps.

Matching a filename is not by itself permission to remove an authored record:
some matches carry intentional celestial seam policy, especially
discontinuous boundaries, and some paths may be deliberate overrides.

Scope

• Audit every authored map header, using the exact Classic filename rules and
  existing-file check.
• Remove horizontal tile_path_1 through tile_path_8 records, plus their
  paired boundary records, when the filename-derived link is the intended
  topology and no authored boundary policy or override must be retained.
• After atrinik/classic#530
  establishes the vertical contract, apply the same review to
  tile_path_9 and tile_path_10.
• Keep explicit paths for intentional overrides, policy-bearing seams, maps
  without a safely parseable coordinate suffix, missing filename neighbors,
  and any vertical stack that has not passed the new runtime contract.
• Do not rename legacy maps or rewrite arbitrary references just to make them
  eligible; handle that as a separately reviewed migration if needed.
• Add a deterministic audit/validation guard so newly authored maps do not
  reintroduce filename-redundant tiling metadata.

Acceptance criteria

• Eligible maps contain no redundant manual tiling records after the full
  horizontal and vertical review; preserved records have a documented reason.
• No celestial_boundary_N remains without its authored tile_path_N, and no
  intentional seam policy is lost.
• The collected Classic-target artifact has the same resolved topology and
  validated exit behavior as before, including terminal edges, signed
  coordinates, explicit overrides, and vertical stack dimensions/reciprocity.
• Run the content validator, python3 tools/validate.py, the relevant Classic
  target/runtime tests, and git diff --check.

Ownership

This is an authored-content change on atrinik/content main; its Classic
target artifact must be validated from the same source revision.