docs: water sections (WBID/WBTB/WSRF), no-BSIN rationale, SkipRoads + water stage in READMEs (terrain-water task 03)

Byte-accurate entries for the three water sections (transitional
per-body level rule, provisional salinity, WSRF sentinel/quantization),
updated size math (~576 MiB at 8K with water), the on-the-record
rationale for NOT serializing basins, and README updates for the new
pipeline stage, the 0_water snapshot, and the SkipRoads toggle.

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

Tools/README.md

@@ -17,6 +17,10 @@ Builds the topographical and logistical foundation of the island before any 3D e
 - **Topography:** FastNoiseLite plus distance-falloff maths for a guaranteed mainland island, a
   mountain spine, dynamic temperature-driven sea level, and an impact crater pushed into the northern
   coast (carved at 80 % of its radius so a landbridge always survives).
+- **Water bodies:** the classified water promoted into explicit blueprint data (ocean + labeled
+  lakes with transitional per-body levels — `WBID`/`WBTB`/`WSRF` sections), plus priority-flood
+  basin diagnostics. The `SkipRoads` config toggle turns a full ~26-min generation into a ~80 s
+  road-less iteration cycle.
 - **Logistics:** `AStarGrid2D` pathfinding producing a looping continental highway, a branch to the
   mountain hub, and county roads daisy-chained outward with Prim's algorithm. Paths are decimated
   (Ramer–Douglas–Peucker) then smoothed (4 Chaikin passes).

Tools/Scripts/README.md

@@ -15,10 +15,18 @@ Generates the entire 2D blueprint. Roughly in order:
    inland lakes; a mainland fill guarantees one contiguous landmass.
 4. **The crater** — placed along the northern coast and carved to below sea level, but only out to
    **80 % of its radius**, which guarantees a landbridge rather than severing the island.
-5. **Biomes and towns** — biome zoning by height and temperature; tiered town placement (Capitol,
+5. **Water bodies** — promotes the classified water into explicit data: the ocean as body 1, each
+   lake connected-component labeled (same 4-connectivity as the true-ocean fill), one transitional
+   surface level per body. Classification comes from the shared `IsOceanPixel`/`IsLakePixel`
+   predicates that the biome stage also uses, so the two can never disagree. A priority-flood
+   pit-fill runs here as validated diagnostics (basin statistics to console; serializes nothing).
+   Drops the `0_water` snapshot.
+6. **Biomes and towns** — biome zoning by height and temperature; tiered town placement (Capitol,
    Hubs, Villages, Outposts, POIs) filtered by slope, water proximity and spacing.
-6. **Roads** — see below.
-7. **Export** — writes the `.dat` blueprint (dual-write: the v2 tagged container under the primary
+7. **Roads** — see below. Skipped entirely when the `SkipRoads` config toggle is on (the ~25-min
+   A\* pass is the bottleneck; a skip run exports a road-less iteration blueprint in ~80 s with a
+   loud console banner).
+8. **Export** — writes the `.dat` blueprint (dual-write: the v2 tagged container under the primary
    seed name, plus the legacy v1 format beside it as `_v1.dat` — see
    `Core/Scripts/BLUEPRINT_FORMAT.md`), then renders the PNG snapshot. The v2 file embeds the
    resolved generation params (seed, MapSize, crater radius, density, impact centre, provenance).
@@ -55,8 +63,10 @@ Road colours on the snapshot, useful for identifying a road: **red** = Highway,
 **dark brown** = Rugged, **light brown** = Trail.
 
 ### Outputs
-`MapData_Seed_<seed>.dat` (v2), `MapData_Seed_<seed>_v1.dat` (legacy dual-write), and
-`Map_Seed_<seed>.png`, all to `user://`.
+`MapData_Seed_<seed>.dat` (v2), `MapData_Seed_<seed>_v1.dat` (legacy dual-write), and the staged
+snapshots `Map_Seed_<seed>_{0_water,1_biomes,2_towns,3_roads}.png`, all to `user://`. (`0_water`
+is painted from the water stage's own outputs — ocean deep blue, lakes lighter blue, land neutral;
+`3_roads` is absent on a SkipRoads run.)
 
 ## `RoundTripHarness.cs`