fix: accept kwargs in capture_exception so $exception_fingerprint is preserved

[posthog]

Summary

PostHog::Client#capture_exception used a positional-only signature, while the rest of the SDK (e.g. capture(attrs)) takes a kwargs Hash. When users naturally followed the kwargs convention:

PostHog.capture_exception(e, distinct_id: current_user.id, properties: { '$exception_fingerprint' => 'CustomGroup' })

…Ruby coerced {distinct_id:, properties:} into the second positional parameter, so:

• distinct_id became a Hash (truthy, so the ||= SecureRandom.uuid fallback didn't fire)
• additional_properties stayed {} and the merge silently dropped every custom property — including $exception_fingerprint, breaking documented Error Tracking custom grouping.

Fix

capture_exception now accepts both forms:

• Positional (existing): capture_exception(e, 'user-123', { 'foo' => 'bar' })
• Kwargs (new): capture_exception(e, distinct_id: 'user-123', properties: { 'foo' => 'bar' })

Internal callers in posthog-rails (active_job.rb, error_subscriber.rb, capture_exceptions.rb) all use the positional form and are unaffected.

The posthog-rails README example is updated to the kwargs form, with $exception_fingerprint shown explicitly.

Test plan

• CI: existing positional spec still passes
• CI: new kwargs spec covering $exception_fingerprint passes
• Manual: call PostHog.capture_exception(e, distinct_id: 'u', properties: { '$exception_fingerprint' => 'g' }) and confirm the property reaches the backend
• Confirm no regression in posthog-rails auto-capture (still uses positional form)

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Created with PostHog Code

[github-actions]

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