Add workflow timeline actor and event-type filters with tests

[akgohain]

Motivation

• Provide timeline filtering controls (actor + event-type text) to aid debugging and study review while keeping the default full timeline visible when no filters are applied.
• Centralize filter state so multiple components can reuse or extend filtering behavior.

Description

• Added a WorkflowTimelineFilterContext provider exposing filters, setActorFilter, setEventTypeFilter, and clearFilters to centralize filter state.
• Implemented WorkflowTimelineFilters UI with actor options (all/user/agent/system), an event-type text input, and a clear/reset button, using a simple native select to avoid test environment issues.
• Implemented WorkflowTimeline which applies filters with useMemo for efficient filtering of long event lists and preserves the full timeline view when filters are empty.
• Added unit tests covering default full timeline, combined actor + event-type filtering, and clear/reset behavior, and added a test script to client/package.json to run the suite.

Testing

• Ran npm --prefix client test -- --watchAll=false --runInBand workflowTimelineFilters and the new test suite passed (3/3 tests).
• Ran npm --prefix client run build and the production build completed successfully (build succeeded with unrelated ESLint warnings reported).

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Codex Task

[akgohain]

Consolidated into draft PR #165 (feat/codex-wave-integration). Closing this source draft to keep review in one place.