Surface per-task status summary in Helix JobContext

[LZD-PratyushBhatt]

When a Task Framework job is configured with a high FailureThreshold so that every partition task is allowed to run to completion, the job's own status flag stays COMPLETED even if individual tasks fail. That masks partial failures: operators watching only the job state cannot tell that some partitions errored, aborted, or timed out.

This adds an aggregated, job-level task status summary that the controller computes and writes into the JobContext when a job reaches a terminal state (completed, failed, or timed out). The summary carries completed/failed counts, a per-state breakdown, and the list of failed partitions, so partial failures stay visible even when the job flag is COMPLETED. Reading the summary is a clean alternative to the Integer.MAX_VALUE FailureThreshold workaround.

helix-core:

• JobContext#updateTaskStatusSummary computes the summary from per-partition states and stores it as the TASK_STATUS_SUMMARY simple field (JSON); JobContext#getTaskStatusSummary reads it back.
• AbstractTaskDispatcher invokes it at the three terminal choke points (markJobComplete, failJob, handleJobTimeout).

helix-front:

• Job detail view gains a "Task Summary" tab that parses TASK_STATUS_SUMMARY and highlights failures.

Tests:

• TestJobTaskStatusSummary integration test (job COMPLETED, summary reports the failures).
• JobTaskSummaryDriver standalone end-to-end driver (runs against a live ZK).
• job-detail component specs for the new getters.

Locally tested in real helix cluster:

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