SxExpr aser wire format fix + Playwright test infrastructure + blob protocol

Aser serialization: aser-call/fragment now return SxExpr instead of String.
serialize/inspect passes SxExpr through unquoted, preventing the double-
escaping (\" → \\\" ) that broke client-side parsing when aser wire format
was output via raw! into <script> tags. Added make-sx-expr + sx-expr-source
primitives to OCaml and JS hosts.

Binary blob protocol: eval, aser, aser-slot, and sx-page-full now send SX
source as length-prefixed blobs instead of escaped strings. Eliminates pipe
desync from concurrent requests and removes all string-escape round-trips
between Python and OCaml.

Bridge safety: re-entrancy guard (_in_io_handler) raises immediately if an
IO handler tries to call the bridge, preventing silent deadlocks.

Fetch error logging: orchestration.sx error callback now logs method + URL
via log-warn. Platform catches (fetchAndRestore, fetchPreload, bindBoostForm)
also log errors instead of silently swallowing them.

Transpiler fixes: makeEnv, scopePeek, scopeEmit, makeSxExpr added as
platform function definitions + transpiler mappings — were referenced in
transpiled code but never defined as JS functions.

Playwright test infrastructure:
- nav() captures JS errors and fails fast with the actual error message
- Checks for [object Object] rendering artifacts
- New tests: delete-row interaction, full page refresh, back button,
  direct load with fresh context, code block content verification
- Default base URL changed to localhost:8013 (standalone dev server)
- docker-compose.dev-sx.yml: port 8013 exposed for local testing
- test-sx-build.sh: build + unit tests + Playwright smoke tests

Geography content: index page component written (sx/sx/geography/index.sx)
describing OCaml evaluator, wire formats, rendering pipeline, and topic
links. Wiring blocked by aser-expand-component children passing issue.

Tests: 1080/1080 JS, 952/952 OCaml, 66/66 Playwright

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

hosts/ocaml/lib/sx_types.ml

@@ -393,7 +393,18 @@ let rec inspect = function
   | Number n ->
     if Float.is_integer n then Printf.sprintf "%d" (int_of_float n)
     else Printf.sprintf "%g" n
-  | String s -> Printf.sprintf "%S" s
+  | String s ->
+    let buf = Buffer.create (String.length s + 2) in
+    Buffer.add_char buf '"';
+    String.iter (function
+      | '"'  -> Buffer.add_string buf "\\\""
+      | '\\' -> Buffer.add_string buf "\\\\"
+      | '\n' -> Buffer.add_string buf "\\n"
+      | '\r' -> Buffer.add_string buf "\\r"
+      | '\t' -> Buffer.add_string buf "\\t"
+      | c    -> Buffer.add_char buf c) s;
+    Buffer.add_char buf '"';
+    Buffer.contents buf
   | Symbol s -> s
   | Keyword k -> ":" ^ k
   | List items | ListRef { contents = items } ->