[$25 BOUNTY] [Perl] Add log watchdog malformed JSON fixture coverage

[leo202000]

Summary

Adds malformed JSON fixture coverage for the v2 log watchdog summary output, as requested in issue #6.

Changes

• v2/scripts/log_watchdog.pl:

  • Add --scan mode: process log files once and exit (non-daemon), suitable for CI and fixture testing.
  • Add --json-summary flag: output JSON summary with json_lines count, malformed_json count, alerts_sent, version, and pattern_matches.
  • Add JSON line detection in process_line: lines starting with { are parsed with JSON::PP; malformed JSON is counted but does not crash the watchdog.
  • Exit code 1 when malformed JSON detected, 0 otherwise.
  • Make File::Tail optional (not needed for --scan mode).
  • Fix pre-existing compile errors: add MAGIC_NUMBER_47 constant, fix $PID_FILE and $DEFAULT_CONFIG bareword usage under use strict.

• v2/scripts/test_watchdog_fixtures.pl (new): 25 tests covering:

  • Valid JSON log lines (3 lines, 0 malformed, exit 0)
  • Malformed JSON log lines (4 lines, all malformed, exit 1)
  • Mixed valid + malformed + plain text (4 JSON-like, 2 malformed, exit 1)
  • Plain text only (0 JSON lines, exit 0)
  • Empty file (0 JSON lines, exit 0)
  • JSON summary field completeness (version, json_lines, malformed_json, alerts_sent, pattern_matches)

• docs/OPERATIONS.md: Documented --scan/--json-summary usage, JSON output format, malformed JSON handling, and fixture test command.

Testing

• perl v2/scripts/test_watchdog_fixtures.pl — 25 tests, all pass (WSL Ubuntu, Perl 5.38.2)
• python3 build.py — diagnostic build log generated and included below
  • Build results: frontend PASS, frailbox PASS, engine PASS (3/10 modules; 7 FAIL due to missing toolchains)

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR (diagnostic/build-9fcca4fe.logd)
• Changes are scoped to the PR purpose
• Security, privacy, and error-handling implications have been considered

Closes #6