fix(omp): discover title-first session transcripts

[jbspeakr]

Summary

Fixes #845 by changing shared Pi/OMP JSONL discovery to find the first type: "session" record rather than requiring it on the first physical line.

OMP may store mutable session titles as a fixed-width type: "title" record before the JSONL session header. CodeBurn previously rejected these otherwise valid transcripts before parsing.

Changes

• Replaced first-line-only session detection with a JSONL scan for the first session record.
• Skips blank lines, malformed JSON, and non-session metadata—including OMP title slots.
• Preserves the existing readSessionFile() read-size and error behavior.
• Adds a regression fixture with a title record and blank line before the session header.
• Renames Pi/OMP negative-test wording: files are rejected only when they contain no session record.

Testing

• I have tested this locally against real data (not just unit tests)
• npm test passes
• npm run build succeeds

For new providers only:

• I installed the tool and generated real sessions by using it
• npm run dev -- today shows correct costs and session counts for this provider
• npm run dev -- models --provider <name> shows correct model names and pricing
• Screenshot or terminal output attached below proving it works with real data