feat(rewards): allocate OSS emissions by repository emission share

[volcano303]

Summary

• Convert repository allocation from per-PR weight multiplier semantics to bounded repo-level emission_share allocation semantics.
• Add issue_discovery_share per repository and apply within-repo PR/issue sub-slice spill logic.
• Collapse top-level emissions to scoring pool + treasury (OSS_EMISSION_SHARE = 0.90, ISSUES_TREASURY_EMISSION_SHARE = 0.10) and route slack to recycle via allocation-time logic.
• Neutralize per-PR repo multipliers in OSS and issue-discovery scoring paths (repo_weight_multiplier / discovery_repo_weight_multiplier set to 1.0 in scoring).
• Add load-time validation and tests for share bounds and sum invariants, plus allocation behavior tests for spill and recycle routing.
• Migrate master_repositories.json to emission_share and issue_discovery_share fields.

Related Issues

Closes #1215

Type of Change

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

Testing

• Tests added/updated
• Manually tested

Commands run:

uv run pytest tests/validator/test_load_weights.py tests/validator/test_emission_allocation.py tests/validator/oss_contributions/mirror/test_scored_pr.py tests/validator/oss_contributions/mirror/test_scoring.py tests/cli/test_miner_score.py -q
uv run ruff check gittensor/validator/utils/load_weights.py gittensor/validator/forward.py tests/validator/test_load_weights.py tests/validator/test_emission_allocation.py
uv run ruff format --check gittensor/validator/utils/load_weights.py gittensor/validator/forward.py tests/validator/test_load_weights.py tests/validator/test_emission_allocation.py

Checklist

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

Recycle Behavior Note

This changes recycle from a fixed baseline (RECYCLE_EMISSION_SHARE) to derived slack behavior:

• Registry-level slack: if sum(emission_share) < 1.0, shortfall is routed to recycle.
• Repo-level inactivity: if both PR and issue-discovery sides are inactive/non-scoring for a repo, its repo slice is routed to recycle.
• If registry sums to 1.0 and all repos are active on at least one side, recycle receives 0 from the scoring pool path.

[anderdc]

Not advancing for #1215 review. Closing.