Multiple fixes and enhancements across the scanner, DB, tests, and docs:
- Surface stream read errors immediately in grype/trivy/syft flows to avoid masking I/O failures behind exit-code messages.
- Improve ringBuffer to handle non-positive capacity, preallocate buffer, and copy trailing bytes to allow GC of large backing arrays.
- Use os.OpenFile with explicit flags/mode when writing log files.
- Make parseIntSetting accept a per-setting default, trim and atoi the value, and return the supplied default for missing/malformed/non-positive values; update DB to pass appropriate defaults.
- Introduce package-level heartbeatTickInterval (default 5s) so tests can shorten the cadence; update heartbeat tests to use a helper and assert progress behavior.
- Test and test helper fixes: countingWriter, file writes check errors, additional assertions, and strengthened manager_test to exercise each env var separately.
- Frontend tests updated for explicit ScannerConfig typing, rename pollInterval to pollIntervalMinutes, add onNewCVEs notification flag, and minor expectations adjustments.
- README: correct docker image reference.
These changes improve error visibility, resource handling, test robustness, and tighten parsing of numeric settings.
