Fix isomorphic SSR: revert inline opcodes, add named let compilation, fix cookie decode

Three bugs broke island SSR rendering of the home stepper widget:

1. Inline VM opcodes (OP_ADD..OP_DEC) broke JIT-compiled functions.
   The compiler emitted single-byte opcodes for first/rest/len/= etc.
   that produced wrong results in complex recursive code (sx-parse
   returned nil, split-tag produced 1 step instead of 16). Reverted
   compiler to use CALL_PRIM for all primitives. VM opcode handlers
   kept for future use.

2. Named let (let loop ((x init)) body) had no compiler support —
   silently produced broken bytecode. Added desugaring to letrec.

3. URL-encoded cookie values not decoded server-side. Client set-cookie
   uses encodeURIComponent but Werkzeug doesn't decode cookie values.
   Added unquote() in bridge cookie injection.

Also: call-lambda used eval_expr which copies Dict values (signals),
breaking mutations through aser lambda calls. Switched to cek_call.

Also: stepper preview now includes ~cssx/tw spreads for SSR styling.

Tests: 1317 JS, 1114 OCaml, 26 integration (2 pre-existing failures)

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

hosts/ocaml/lib/sx_vm.ml

@@ -418,7 +418,12 @@ and run vm =
           push vm (match a, b with Number x, Number y -> Number (x /. y) | _ -> Nil)
         | 164 (* OP_EQ *) ->
           let b = pop vm and a = pop vm in
-          push vm (Bool (a = b))
+          (* Must normalize ListRef→List before structural compare,
+             same as the "=" primitive in sx_primitives.ml *)
+          let rec norm = function
+            | ListRef { contents = l } -> List (List.map norm l)
+            | List l -> List (List.map norm l) | v -> v in
+          push vm (Bool (norm a = norm b))
         | 165 (* OP_LT *) ->
           let b = pop vm and a = pop vm in
           push vm (match a, b with Number x, Number y -> Bool (x < y) | String x, String y -> Bool (x < y) | _ -> Bool false)