feat(observability): add scanner-level skip and filter messages

[quanticsoul4772]

Closes #32

What this changes

Previous attempt (#35) adjusted the global log level — this PR instead adds targeted messages at the scanner level, specifically where scans are skipped, partially executed, or findings are filtered without user visibility.

docker_scout_scanner.py

• No container files found: when neither Docker Compose nor Kubernetes files are detected, prints [i] No Docker Compose or Kubernetes files found — container scan skipped. so users know container scanning was intentionally skipped, not broken or forgotten.
• Negligible CVE filter: counts Negligible-severity CVEs that are suppressed and prints [i] Filtered N Negligible-severity CVE(s) from Docker Scout results (use --verbose to include them). so users can distinguish "0 findings" from "findings were suppressed".

grype_scanner.py

• Negligible CVE filter: same filter-count message as above, for the Grype fallback path.

parser.py (scan_directory_level)

• Unreadable files warning: counts files that fail to open during directory-level scanning and prints [!] Warning: N file(s) could not be read and were skipped — scan results may be incomplete. This is the inverse-regex scanner path where silent file-read failures mean the "required pattern" check runs on incomplete data.

Example output

Container scan skipped (no files):

[i] No Docker Compose or Kubernetes files found — container scan skipped.

After container scan with filtered CVEs:

[i] Filtered 14 Negligible-severity CVE(s) from Docker Scout results (use --verbose to include them).

After directory scan with unreadable files:

[!] Warning: 2 file(s) could not be read and were skipped — scan results may be incomplete.

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