fix(web): support sandbox deployment routing

[jialudev]

Summary

• Resolve frontend assets, favicon, shared worker, and API requests relative to the current mount point so the web UI can run behind sandbox path prefixes.
• Switch the SPA to hash routing to avoid server-side route fallback assumptions in sandbox deployments.
• Use registry/name Hub template routes instead of encoded slash IDs so template detail and workspace file requests survive proxy and sandbox routing layers.

Testing

• Not run by Codex in this PR creation step; user reports this branch was tested locally.

[RussellLuo]

LGTM