docs: drop stale npm install -g rescript + npx rescript-legacy -w refs (#67)

Follows panll#65 (npm→Deno migration) and panll#66 (docs sweep).

- docs/developer-guide.md: remove global rescript install step;
  ReScript is now resolved via deno.json `npm:rescript@^12.0.0` on first
  `deno task res:build`. Reword surrounding prose to reflect this.
- docs/guides/QUICKSTART-FOR-SON.md: `npx rescript-legacy -w` →
  `deno task res:watch`.

Surfaced by panll#66 meander.

Author: hyperpolymath

docs/developer-guide.md

@@ -91,11 +91,10 @@ source $HOME/.cargo/env
 curl -fsSL https://deno.land/x/install/install.sh | sh
 export DENO_INSTALL="/home/$USER/.deno"
 export PATH="$DENO_INSTALL/bin:$PATH"
-
-# Install ReScript
-npm install -g rescript
 ```
 
+ReScript is pinned in `deno.json` (`npm:rescript@^12.0.0`) and resolved on first `deno task res:build` — no global install required.
+
 ### Clone and Build
 
 ```bash

docs/guides/QUICKSTART-FOR-SON.md

@@ -16,7 +16,7 @@ On top of these, there are **overlay panels** you can open from the panel bar (v
 cd ~/Documents/hyperpolymath-repos/panll
 
 # Terminal 1: Start the ReScript compiler (watches for changes)
-npx rescript-legacy -w
+deno task res:watch
 
 # Terminal 2: Bundle the JS and serve
 just bundle && just serve:dev