Add log watchdog malformed JSON fixtures

[h1065153539-create]

Summary

• Adds --json-summary FILE to v2/scripts/log_watchdog.pl for offline newline-delimited JSON log validation without starting watch/daemon mode.
• Counts valid, malformed, empty, and JSON value-shape records while reporting malformed line numbers and parser errors only.
• Adds valid, malformed, and mixed fixtures plus a lightweight Perl fixture harness, and documents the command/exit-code behavior in docs/OPERATIONS.md.

Validation

• perl -c v2/scripts/log_watchdog.pl passed.
• perl v2/scripts/test_log_watchdog_json_summary.pl passed.
• perl v2/scripts/log_watchdog.pl --json-summary v2/fixtures/log_watchdog_mixed.log returns exit code 2 as expected for malformed records and emits parseable JSON.
• python3 build.py -m v2-market-stream was attempted locally, but the diagnostic build path hung/timed out in this API-sourced subset; focused validation output and the blocker are recorded in diagnostic/build-6fbee95d.logd and diagnostic/build-6fbee95d.json.

Security

• The summary intentionally omits raw log lines, so malformed records containing secret-like fields such as token or password are not echoed.
• Default watchdog output and daemon/watch behavior remain compatible; File::Tail is loaded only when watch mode is used.

Closes #6

[Soengkit]

Closing this PR because the linked fork issue is only a closed payout tracker for an already submitted upstream PR. This fork is not an active bounty intake or payment authority, and it is not accepting external submissions or payment details here.