Step 16: Fix client routing — prefix-agnostic SX URL matching

The /sx/ prefix mismatch: defpage declares paths like /language/docs/<slug>
but browser URLs are /sx/(language.(doc.slug)). find-matching-route used
starts-with? "/(", missing the /sx/ prefix entirely.

Fix: find-matching-route now uses (index-of path "/(") to detect the SX
URL portion regardless of prefix. Works for /sx/, /myapp/, any prefix.
No hardcoded paths.

Also fixed deps-satisfied?: nil deps (unknown) now returns false instead
of true, preventing client-side eval of pages with unresolved components.
Correctly falls back to server fetch.

Verified with Playwright: clicking "Getting Started" on the docs page now
shows "sx:route deps miss for docs-page" → "sx:route server fetch" instead
of the old "sx:route no match (51 routes)".

2 new router tests for prefix stripping. 2914/2914 total, zero failures.

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

shared/static/wasm/sx_browser.bc.wasm.js

@@ -1792,7 +1792,7 @@
             blake2_js_for_wasm_create: blake2_js_for_wasm_create};
    }
    (globalThis))
-({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["sx-7dd7570e",[2]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,4]],["dune__exe__Sx_browser-19f4e198",[2,3,5]],["std_exit-10fb8830",[2]],["start-f5d3f095",0]],"generated":(b=>{var
+({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["re-9a0de245",[2]],["sx-1549dd9c",[2,3]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,5]],["dune__exe__Sx_browser-cb04d103",[2,4,6]],["std_exit-10fb8830",[2]],["start-f808dbe1",0]],"generated":(b=>{var
 c=b,a=b?.module?.export||b;return{"env":{"caml_ba_kind_of_typed_array":()=>{throw new
 Error("caml_ba_kind_of_typed_array not implemented")},"caml_exn_with_js_backtrace":()=>{throw new
 Error("caml_exn_with_js_backtrace not implemented")},"caml_int64_create_lo_mi_hi":()=>{throw new