Remove the build-gate probe accidentally committed to main.tsx

Copilot caught this. `scripts/verify-build-gate.mjs` appends a
`node:fs` import to `clients/web/src/main.tsx`, asserts the
browser-externalized-builtin gate rejects it, then restores the file.
Round 6 was committed with `git add -A` while `local:gate` was mid-run,
so the staged snapshot caught the probe in place and shipped it.

The consequence is exactly what the gate exists to prevent: a Node
built-in in the normal browser graph, which makes the gate fail every
Vite build from here on. CI could not have passed.

`main.tsx` is restored byte-for-byte to its v2/main content; no other
file was affected.

The transferable lesson, and the reason this is its own commit rather
than a squash: **never stage with `git add -A` while the gate is
running.** `verify:build-gate` mutates a tracked source file for the
length of one build, and that window is wide enough to catch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EQVdemwgUhh45yzeaRSLhW
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/main.tsx

@@ -21,6 +21,3 @@ createRoot(document.getElementById("root")!).render(
     </MantineProvider>
   </StrictMode>,
 );
-
-import * as __nodeBuiltinProbe from "node:fs";
-if (globalThis.__never__) console.log(__nodeBuiltinProbe);