feat: add --verbose flag and improve error messaging

[quanticsoul4772]

Summary

Addresses #32 — InfraScan should be more verbose.

• New -v / --verbose flag — sets logging to DEBUG level and enables richer output
• Verbose startup info — prints resolved framework, output format, and --download-external-modules state before scanning
• Verbose scan summary — prints resource count and finding count as soon as the scanner finishes
• Better error messages — regular path now shows [ERROR] Scan failed: <reason> + a hint to rerun with --verbose for the full traceback (previously required setting DEBUG externally)
• Consistent prefix style — [ERROR], [INFO], [*] prefixes make log lines easier to grep in CI output

Example output

Normal run:

[*] Scanning '/path/to/infra' with scanner: 'comprehensive' ...

Verbose run:

[*] Scanning '/path/to/infra' with scanner: 'comprehensive' ...
[*] Framework: auto
[*] Output format: text
[*] Download external modules: False
[*] Scan complete: 12 resource(s) found, 3 finding(s)

Error (normal):

[ERROR] Scan failed: <message>
[INFO]  Run with --verbose (-v) for a full traceback and debug output.

Error (verbose):

[ERROR] Scan failed: <message>
[INFO]  Run with --verbose (-v) for a full traceback and debug output.
Traceback (most recent call last):
  ...

🤖 Generated with Claude Code

[jkondrat]

This doesn't fully address the original issue.

The main concern in #32 was improving visibility into what the scanners are actually doing, especially in cases where scans are skipped, partially executed, or fail silently. This PR mostly adjusts the global logging level, but it doesn’t significantly improve scanner-level observability.