fix(web): allow docker host callbacks in local development

[FradSer]

Summary

Allow the exact host.docker.internal Host header in the local Vite development proxy.

Why

Local Sandbox callbacks reach the console/API proxy through Docker's host alias. Vite rejects that Host with HTTP 403 before forwarding the request. Add the exact alias so callbacks can reach the development stack.

Extracted from the unrelated local-development changes removed from #693 at review request 6. Existing issues and PRs were searched; no dedicated open issue was found. No issue is closed by this PR.

Verification

• just fmt-check; focused Vite config lint; just commit-check.
• Started the actual development server locally: a request with Host: host.docker.internal returns HTTP 200; Host: unrelated.example still returns HTTP 403.
• Exact-head just check was attempted on local Linux (Bun 1.4.0): format/docs/lint/type stages passed; the unchanged Driver backpressure fixture failed (openai-app-server-client.test.ts:2055; 2,281 passed / 47 skipped / 1 failed). This initial full-gate failure is retained, not claimed as a pass.
• Fresh Host-header acceptance passed again (200 for the exact alias, 403 for an unrelated host). All three shared Driver failure cases pass in isolation; the identical Driver pin also passed the complete #699 hosted gate. No Driver change is included.
• Full hosted CI is triggered by Ready for review; see Checks for this PR’s own result. Full Sandbox/model execution was not run.

Review

• Closest review area: Vite's development server.allowedHosts.
• Env/config changes: one exact local hostname, without a wildcard or unrestricted host setting.
• Known trade-offs: applies to the dev server only.

Impact

• Generated files / GraphQL / DB / lockfile: N/A; unchanged.
• Risk and rollback: revert this isolated commit. No deployment or migration.

Design

N/A: no product UI changes.