DPBG/Engram.AI: add label_multipliers

[Lobster-0429]

Weight Adjustment PR

Changes Summary

Metric	Total
Repositories Added	0
Repositories Removed	0
Weights Modified	0
Net Weight Change	0

Justification

Adds per-label PR scoring multipliers to DPBG/Engram.AI. This does not touch emission_share (stays 0.0025) or any other repository — the total registry emission_share remains 1.0. It only changes how individual merged PRs in this repo are weighted by label.

New label_multipliers:

Label	Multiplier
feature	1.0
enhancement	0.7
bug	0.5
refactor	0.2
chore	0.1

Unlabelled PRs keep the neutral default_label_multiplier (1.0). Verified the registry still loads and passes emission/eligibility/scoring validation.

Additional Acceptable Branches

• No additional_acceptable_branches changes in this PR
• Proof of merged PR(s) provided above for all additional_acceptable_branches entries

Checklist

• Changes summary table is filled in accurately
• Net weight changes are justified in the Justification section
• Added repositories have correct branch and initial weight