fix(cursor): parse current transcript envelopes

[adel-pplx]

Summary

• parse current Cursor transcripts that wrap text and tool blocks under message.content
• preserve source-faithful evidence pointers and existing top-level transcript shapes
• ignore turn_ended bookkeeping instead of reporting an unknown record

Reproduction

With Cursor 3.14.27, three local transcripts previously emitted zero events and three warnings. They now emit 12 normalized events with no parser warnings.

Verification

• go test ./...
• go test -race ./...
• go vet ./...
• golangci-lint run and fmt --diff (v2.12.2)
• FuzzCursorExtract for 15 seconds
• local Cursor scan and timeline

Addresses the remaining Cursor item in #6.

[thom-pplx]

LGTM, just one minor comment.