Fix Daytona sandbox reachability probe for Cloudflare quick-tunnel webapp targets (#51)

[alanzabihi]

Summary

• Replaces the single-shot curl probe in prepareWebappTarget() with a retrying probe (probeWebappTarget()): 5 attempts, 10 s timeout, exponential backoff (1/2/4/8 s).
• Parses the HTTP status code in JS instead of a shell pipeline so diagnostics are clean and curl exit codes are preserved.
• Fails fast with a clear error message and per-attempt diagnostics when the URL remains unreachable, removing the misleading autobrin-flue#158 reference.

Context

The Daytona sandbox cannot always reach Cloudflare quick-tunnel URLs immediately. This change absorbs transient DNS propagation delays and makes the real blocker (network reachability / outbound filtering) explicit in the error output instead of blaming a closed issue.

Test plan

• npx vitest run tests/daytona-bootstrap.test.ts passes.
• Full suite npx vitest run passes (313 tests).
• npm run typecheck passes.
• Bugbot review found no bugs.

Limitation / follow-up

If Cloudflare is actively blocking the sandbox's outbound network, retries alone will not help. A longer-term fix may require changing the tunnel mechanism (e.g. a private Daytona network bridge or persistent tunnel). This PR is scoped to the benchpress-side robustness requested in the issue.

[cursor]

Current version of PR was reviewed by /review-bugbot on Jul 3, 13:19 GMT+2. It flagged 0 findings.

^{Bugbot on commit 9722f25 is skipped.}