fix(cli): improve exec eval observability

[wgqqqqq]

Summary

• add stable BITFUN_EXIT diagnostics for CLI exec setup, turn failures, system errors, and patch write failures
• include tool start input previews for main and subagent tool events with data_url redaction and truncation
• create parent directories for --output-patch paths and wait for exec turn settlement before emitting patches
• persist resolved model ids observed by CLI exec events

Notes

• intentionally does not include prompt changes
• intentionally does not include the patch verifier / compile-build gate from evals-on-release
• intentionally does not port the older AI request audit implementation or older exec command runtime patches already superseded on main

Verification

• pnpm run fmt:rs
• cargo check -p bitfun-cli
• cargo test -p bitfun-cli diagnostics -- --nocapture
• cargo test -p bitfun-cli patch_tests -- --nocapture
• git diff --check