Export profiling data in React DevTools Profiler JSON format (version 5)
so it can be imported into the browser extension's Profiler tab.

- New IPC command: profile-export
- New CLI command: profile export <file>
- Maps internal ProfilingSession to ProfilingDataExport schema
- Includes commit data, fiber durations, change descriptions, snapshots

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

processProfilingData() rejected data when stoppedAt was set, but
stopProfilingAndCollect() requests data from renderers asynchronously —
the response often arrives after profiler.stop() has already run,
resulting in 0 commits captured. Remove the stoppedAt guard since the
bridge controls data collection timing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…snapshots

initialTreeBaseDurations only included nodes from the first commit's
fiberSelfDurations, leaving most nodes without a base duration. The
React DevTools flame graph needs an entry for every node to render.

Also fix multi-root export: filter snapshots to each root's subtree
instead of duplicating all nodes across all roots, and restore element
type 11 for root nodes so DevTools recognises them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

key was typed as number | string | null but ComponentNode.key is
string | null — the number case was unreachable.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>