v2.0.0-beta.5 — Harden prompt input and quota reads

Prevent unintended input waits throughout Porch's prompt transports.

• Reject empty or whitespace-only explicit prompts and guidance instead of falling back to inherited stdin. Reject conflicting argument/file sources and empty file-option values.
• Stop shell prompt builders from reading ambient stdin. Close unused stdin for Grok/Devin file-based backend transports.
• Read caller-supplied paths literally, including files named -, in prompt transports, all code-review depths, and judge input.
• Replace costly shell whitespace substitutions so large file prompts remain responsive.
• Reuse the concurrent JSON-RPC client for Codex quota queries, enforcing one response deadline while draining stderr and handling partial response lines.

Compatibility: provide exactly one nonempty argument/file prompt, or supply the prompt through stdin when neither is selected. Review context alongside an explicit question still requires --context-stdin.

Validation: 36 focused input tests and 7 quota tests passed. The full offline harness reports 1001 passed, 0 failed; all backends were fakes. No live provider smoke test was run.