Add reconciled token usage bridge

[QingJunXue]

Summary

• add a single local /token-usage/events bridge without a price endpoint or billing-provider dependency
• reconcile MessagePort, rollout JSONL, subagent rollout files, and protocol-proxy Usage events
• capture Input, Cached Input, Cache Write, Output, Reasoning, request status, retries, and Usage-missing responses
• follow the dynamically selected Helper port and prevent local proxy URLs from becoming upstream URLs
• add bounded stream lifetimes, downstream-disconnect resilience, ledger rotation, and diagnostic-log rotation

Disk and privacy behavior

• rollout files are read fully once, then tailed incrementally
• proxy ledger rotates at 20 MB and retains three archives
• diagnostic logs rotate at 20 MB and retain three archives
• high-frequency successful bridge events are not persisted
• the Usage ledger stores no prompts, response text, API keys, or upstream URLs

Verification

• cargo fmt --all -- --check
• Token Usage tests: 13/13
• Bridge route tests: 27/27
• Protocol proxy tests: 48/48
• Relay configuration tests: 103/103
• Launcher tests: 74/74, with one unrelated Windows symlink-privilege test skipped
• Diagnostic log tests: 3/3
• scoped Clippy: 0 warnings in the new Token Usage implementation
• cargo build --release -p codex-plus-launcher

The skipped launcher test requires Windows symbolic-link privilege and fails with OS error 1314 independently of this change.