feat: implement validated SLaNg token multi-head shared pipeline architecture

[sp25-bai-047-wq]

Completed Deliverables Matrix (Revised & Approved)

All core engineering feedback issues have been structurally addressed on an isolated branch:

1. Real Data Consumption:** Replaced all noise vectors with actual tokenized character embedding sequences (src_seq & tgt_in_seq).
2. Shared Team Architecture:** Aligned class parameters precisely with the team's standard variables (TreeEncoder, TreeDecoder, RuleHead, and StepTracer).
3. 3-Head Loss Function Wired:** Configured joint CrossEntropy and Binary CrossEntropy optimization loss across sequence token generation path, rule classification, and verification logic tracker.
4. Configuration & Documentation Added:** Extracted hyper-parameters into config.json and logged system scale metrics and generation scope boundaries inside DATASET_REPORT.md.

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