fix: wire config logLevel and add 50MB log file rotation (#558)

[MrRealORG]

Summary

Addresses #558 (log files growing to 50GB+ in hours) with two fixes:

1. Config `logLevel` was never applied (bug)

The `logLevel` field was defined in the config schema (`config.ts:99`) and documented for users, but never read at runtime. `Log.init()` in `index.ts` only checked the CLI `--log-level` flag and `Installation.isLocal()`. Users who set `"logLevel": "WARN"` in their config file saw no effect.

Fix: Added `Log.setLevel()` export and called it in `InstanceBootstrap` right after config is loaded. CLI `--log-level` still takes precedence (applied first in middleware), but config file now works as a fallback.

2. No per-file size cap (feature)

Log files grew unbounded via `createWriteStream(path, { flags: "a" })`. A single session could produce tens of GB.

Fix: Added 50MB max file size with automatic rotation:

• Tracks `currentSize` as bytes are written
• When `currentSize + len > MAX_LOG_SIZE`, triggers rotation
• Rotation: closes stream, shifts `.log → .log.1 → .log.2 → ... → .log.9`, truncates original, opens fresh stream
• A `rotating` guard prevents concurrent rotations
• Existing timestamped-file cleanup (keeps 10) continues alongside rotation

Test Plan

• Set `"logLevel": "WARN"` in mimocode.json, verify debug/info messages are suppressed
• Set `"logLevel": "ERROR"`, verify only errors appear
• Verify CLI `--log-level DEBUG` still overrides config
• Run a long session, verify log file rotates at ~50MB
• Verify rotated files (.log.1, .log.2, ...) exist and are valid
• Verify no log messages are lost during rotation