Add reactive runtime demos + sx-web federation plan

7 interactive island demos for the reactive runtime layers:
- L0 Ref (timer + DOM handle), L1 Foreign (canvas via host-call),
  L2 Machine (traffic light), L3 Commands (undo/redo),
  L4 Loop (bouncing ball), L5 Keyed Lists, L6 App Shell

Fix OCaml build: add (wrapped false) to lib/dune, remove Sx. qualifiers.
Fix JS build: include dom-lib + browser-lib in adapter compilation.

New plan: sx-web federated component web — browser nodes via WebTransport,
server nodes via IPFS, in-browser authoring, AI composition layer.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/lib/dune

@@ -1,2 +1,3 @@
 (library
- (name sx))
+ (name sx)
+ (wrapped false))