[codex] preserve HTTP proxy path delimiters

[guiwenlingmu962-bot]

Summary

• build HTTP proxy download targets with the URL API instead of string concatenation
• preserve spaces, ?, and # as encoded path data
• preserve query parameters already configured on the proxy target
• add focused and end-to-end regression coverage

Root cause and impact

The previous string concatenation treated ? and # in a file path as URL query and fragment delimiters. It could also append the separator after a proxy target's existing query string. As a result, valid proxied file names could fetch the wrong URL or return 404.

The new helper appends to URL.pathname, which percent-encodes path delimiters while leaving the configured query string intact.

Validation

• bun test — 31 passed
• bun test tests/routes/file-proxy03.test.ts --timeout 50000 — 6 passed
• bun x tsc --noEmit --pretty false
• bun x biome format lib/utils/resolve-file-proxy.ts tests/routes/file-proxy03.test.ts
• git diff --check

bun run build remains blocked on Windows by the existing Winterspec absolute-path backslash parsing issue; the tests and TypeScript check pass.

/claim #5