Title:feat(viewer): Implement Orchestrator Graph View

[faranjit]

This PR implements the core visual "Orchestrator Graph" feature and fixes several critical bugs in the "List" view. It also introduces a major type-safety refactor to stabilize the codebase.

1. New: Orchestrator Graph View

• Implements the new "Graph" view, completing our primary visualization feature.
• Adds @xyflow/react for rendering and dagre for auto-layout.
• Creates graphLayout.ts to transform the span forest into a DAG.
• Adds custom, styled and components.
• Adds a "List" / "Graph" toggle to App.tsx.

2. Fixes: This PR fixes two major visual bugs:

• Fixed Graph Layout (Orphan Bug)
• Fixed List Hierarchy (Indentation Bug)

3. Core Refactor: AppTracerEvent

• Introduces a hard type-safe boundary for the entire app.
• AppTracerEvent is now the canonical internal type.
• normalizeEvent.ts is a new gatekeeper function that cleans/validates all raw TracerEvent data coming from files or live streams.
• SpanEventStatus now officially includes "streaming".
• All components, hooks, and utils (buildSpanTree, eventFilters, etc.) are refactored to use AppTracerEvent, eliminating all any casts.

4. Tests & Docs

• All existing tests are refactored to use the normalizeEvent helper.
• Adds new tests for normalizeEvent, graphLayout, and the App view toggle.
• Updates README.md with new screenshots.