Uncap watershed detail in the Node binding + sync docs

`6f163fc` widened watershed_detail from u8 to u32 in the core, CLI, and
Python binding but not the Node/wasm binding, which still assigned a u8 to
config.watershed_detail — a wasm build error (E0308). Widen the Node
Options field to u32 and refresh every "0..=255" watershed doc (CLI help,
Config field, .pyi, index.d.ts, and all three READMEs) to reflect that the
level is now uncapped (default 128; higher = more regions).

crates/vtracer-py/vtracer.pyi

@@ -27,7 +27,7 @@ class Config:
         adaptive: bool = False,                # bw: Bradley–Roth adaptive
         adaptive_window: int = 0,              # bw adaptive: window px (0 = auto)
         adaptive_t: float = 15.0,              # bw adaptive: % below local mean
-        watershed_detail: int = 128,           # watershed: cut level 0..=255
+        watershed_detail: int = 128,           # watershed: cut level (higher = more regions, uncapped)
     ) -> None: ...
 
     @staticmethod