[FLINK-40600][runtime-web] Add missing web dashboard specs and tighten thin ones

[spuru9]

What is the purpose of the change

FLINK-40117 added Vitest specs for most of the web dashboard views, but pages/application/overview and pages/application/exceptions still had none. Some of the added specs also only checked that the mocked data was loaded, not what the component derived from it: the timeline spec didn't assert the computed vertex and subtask ranges, the job overview spec never fed a plan into ngOnInit, the cluster overview spec didn't assert the derived statistics, and TaskManagerService only had tests for loadManagers and loadManager. The HumanizeDatePipe test for format 'B' relied on Angular throwing for missing locale data, which an Angular upgrade could change.

This adds the two missing specs and tightens the existing ones so they fail when the derived values change.

Brief change log

• Added application-overview.component.spec.ts and application-exceptions.component.spec.ts.
• Tightened job-timeline.component.spec.ts to assert the computed vertex ranges (including the duration-derived end-time branch and filtering of not-yet-started vertices) and the per-subtask timeline ranges, instead of just checking counts/names.
• Tightened job-overview.component.spec.ts with a new spec that feeds an actual plan into ngOnInit and asserts the derived pendingNodes/pendingLinks and the resulting dagreComponent.flush call.
• Tightened overview.component.spec.ts (cluster overview) to assert the exact derived cluster-statistics object instead of just checking for static label text.
• Expanded task-manager.service.spec.ts from covering only loadManagers/loadManager to covering all public methods.
• Replaced the humanize-date.pipe.spec.ts test that relied on Angular throwing for format 'B' with one driven by an unregistered locale, which is a stable part of Angular's i18n contract rather than a version-dependent implementation detail.

Verifying this change

This change added tests and can be verified as follows:

• npx ng test --watch=false in flink-runtime-web/web-dashboard: 35 spec files / 158 tests pass (up from the prior baseline of 33 files / 139 tests).
• npm run lint and npx prettier --check are clean on all changed/added files.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude Code (claude-sonnet-5)

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CI report:

• 1129e92 Azure: SUCCESS

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