feat(rewards): enforce bounded repo-level emission shares

[Desel72]

Summary

• Renames the repository allocation field from weight to emission_share while keeping a compatibility alias for existing callers.
• Moves repo allocation out of per-PR scoring and into round aggregation, so a repo can receive at most its configured slice of the 90% scoring pool.
• Adds issue_discovery_share with same-repo PR/issue spill behavior: an active side receives the full repo slice, while fully inactive repo slices and registry slack recycle to UID 0.
• Collapses top-level emissions to OSS_EMISSION_SHARE = 0.90 and ISSUES_TREASURY_EMISSION_SHARE = 0.10; removes the fixed recycle baseline.

Related Issues

Fixes #1215

Clean History Note

This is a clean-history resubmission of #1236 after the maintainer flagged the preserved rebase author date. The branch was recreated from latest upstream/test and committed once as a fresh commit with matching author and commit timestamps.

Deliverable Coverage

• emission_share loads as a bounded [0, 1] repo allocation with registry sum <= 1.0.
• Existing registry entries are migrated from weight to emission_share; entrius/oc-1 opts out of issue discovery with issue_discovery_share = 0.0.
• Per-PR repo weighting is neutralized in earned score, collateral score, mirror scoring, and issue discovery; old storage fields remain neutral for compatibility.
• Repo slices are allocated at aggregation, not per PR, so PR volume can only affect distribution inside the repo slice.
• PR/issue sub-slices spill only within the same repo; fully inactive repo slices and registry slack route to RECYCLE_UID.
• Tests cover share bounds, invalid registry sums, fixed repo slices across different PR counts, same-repo spill in both directions, issue_discovery_share = 0.0, full inactivity recycling, and registry slack recycling.

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Testing

• Tests added/updated
• Manually tested

Validation:

• uv run pytest tests/validator/test_emission_share_allocation.py tests/validator/test_load_weights.py tests/validator/oss_contributions/mirror/test_scored_pr.py tests/validator/oss_contributions/mirror/test_scoring.py -q (133 passed)
• uv run pytest tests/ -q (737 passed)
• uv run pre-commit run --all-files --show-diff-on-failure
• SKIP=pytest uv run pre-commit run --all-files --hook-stage pre-push

Checklist

• Code follows project style guidelines
• Self-review completed
• Changes are documented (if applicable)

Notes

Recycle now receives only unclaimed repo slices and registry-level slack; it is no longer a fixed baseline. Round-level rewards remain bounded by the 90% scoring pool plus the 10% treasury allocation.