docs: SeaLevelModel/SeaLevelValue config notes (terrain-water task 04)

Both sea-level modes documented (flat default 0.15 / legacy field
Lerp); noted the blueprint does not record which model produced it —
the WBTB levels are the observable. Batch runner lives in /tmp
(throwaway), not in-repo.

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

Core/Scripts/BLUEPRINT_FORMAT.md

@@ -94,6 +94,18 @@ sections `5·MapSize²` bytes (4 height + 1 biome) ≈ **320 MiB at 8K**, vs v1'
 `9·MapSize²` (adds 2 B `WBID` + 2 B `WSRF`) ≈ **576 MiB at 8K** plus a trivial `WBTB` (20 B per
 body).
 
+### Config knobs that shape blueprint content (not part of the byte format)
+
+- **`SeaLevelModel`** (`"flat"` | `"field"`) + **`SeaLevelValue`** (float; used when flat) —
+  D-033: selects what `MapGenerator.GetSeaLevel` returns. `"flat"` (the default, value 0.15) is
+  one scalar sea level everywhere; `"field"` is the legacy latitude Lerp (0.26 north → 0.15
+  south). Generator-only — all nine `GetSeaLevel` call sites inherit the model; nothing at
+  runtime computes sea level. The model in force shapes the coastline, masks, biomes, water
+  bodies, and `WBTB` levels of the blueprint being generated; the file itself does not record
+  which model produced it (the `WBTB` levels are the observable).
+- **`SkipRoads`** (bool, default false) — exports with present-but-empty road sections (see the
+  road-section table note).
+
 ### Deliberately NOT a section: basins (`BSIN`)
 
 The priority-flood pit-fill that runs in the water-bodies stage is **diagnostics only** and