docs(decisions): address PR #129 review — D-191 §8 amendment + boundary notes

Blocking PR #129 items 1, 2 (plus polish 16 and 17):

- D-191 §8 prose rewritten to match the code. The previous amendment said
  positions were `{x, y}` objects against a "typically 1024 × 512" grid,
  but the generator, the six hand-authored templates, and all 2394
  procedural seed files ship `[row, col]` integer arrays against a
  `{"w": 512, "h": 256}` grid. The decision doc is now aligned with
  reality: positions are `[row, col]`, the storage grid is 512 × 256,
  and the row-first ordering is called out explicitly so readers can
  cross-reference NumPy/flood-fill/A*/cost-grid conventions.

- §8 now follows the D-094 amendment pattern. The superseded 2026-04-10
  prose is preserved verbatim as "Original (superseded)" with a dated
  Amendment block on top — future readers can see what changed and why
  instead of silently losing the history.

- brands.toml header gains a short Phase 2 boundary note. The 4 anchor
  brands come from D-189 §5; the additional ~23 brands from D-189 §11
  are deliberately deferred to Phase 3 — Phase 2 only needs the demand-
  node plumbing and V-B01..V-B06 validation exercised end-to-end.

- systems-schema.sql `bodies.terrain_reference` comment now pins the
  repo-root-relative path convention (wiki/star-systems/<slug>/bodies/
  <body_id>/heightmap.png) so the three downstream pipelines (populate,
  atlas generator, client loader) share a documented contract instead
  of drifting against an unwritten convention.

server/data/systems-schema.sql

@@ -167,7 +167,16 @@ CREATE TABLE IF NOT EXISTS bodies (
     industrial_corridor TEXT,          -- MVG, Gate_Corp, DSMC, Prometheus, Agricultural_Syndic
 
     -- Rendering
-    terrain_reference TEXT,            -- heightmap path when authored, NULL otherwise
+    -- terrain_reference: repo-root-relative path to the body's heightmap PNG.
+    -- Convention (enforced by populate_terrain_reference.py and assumed by
+    -- generate_atlas.py and the Godot client's atlas scene loader):
+    --   wiki/star-systems/<system_slug>/bodies/<body_id>/heightmap.png
+    -- where <system_slug> = system_id with spaces replaced by hyphens
+    -- (e.g. "GJ 244A" → "GJ-244A"). NULL means no heightmap has been
+    -- generated for this body yet. The three downstream pipelines
+    -- (populate, atlas generator, client loader) all assume this format —
+    -- changing it requires updating all three sites together.
+    terrain_reference TEXT,
     screenshot_path TEXT,              -- planetary shader screenshot path
 
     updated_at TEXT DEFAULT (datetime('now'))