Validate optional live-debugger version

[watson]

Motivation

Browser Live Debugger needs a stable build identifier when we want to resolve browser probe results back to uploaded sourcemap metadata, but that value should stay optional so instrumentation can still work when no version is configured.

Changes

This PR updates the Live Debugger build-plugin config to understand an optional liveDebugger.version field.

Before these changes:

• the plugin had no explicit version option
• there was no validation tying Live Debugger config to sourcemap upload config
• the docs did not describe how browser build identity should be configured

With these changes:

• add version?: string to LiveDebuggerOptions
• carry version through the validated options shape
• validate that version is a string when provided
• validate that liveDebugger.version matches errorTracking.sourcemaps.releaseVersion when both are configured
• keep version optional so Live Debugger still works without source-aware browser build lookup
• document the intended version semantics in the plugin README
• update unit tests and the live-debugger e2e fixture to cover the new config behavior

Testing

• yarn test:unit packages/plugins/live-debugger/src/validate.test.ts packages/plugins/live-debugger/src/index.test.ts
• ReadLints reported no linter errors on the changed files

[watson]

• Validate optional live-debugger version #325 👈 (View in Graphite)
• Add live-debugger plugin #296 : 1 other dependent PR (#324 )
• master

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[yoannmoinet]

lgtm