chore(weights): add label multipliers for phase-rs/phase

[plind-junior]

phase-rs/phase was added to the repository whitelist in #1389 with only
emission_share and issue_discovery_share, so every merged PR scored at a
flat 1.0× regardless of label. This adds a label_multipliers block so phase
contributions are weighted by PR type, consistent with the other scored repos.

"phase-rs/phase": {
  "emission_share": 0.015,
  "issue_discovery_share": 0.0,
  "label_multipliers": {
    "bug": 1.1,
    "ai-contribution": 0,
    "enhancement": 1.25,
    "feature": 1.5,
    "refactor": 0.25
  }
}

• Multiplier values follow the entrius/gittensor pattern
  (bug 1.1 / enhancement 1.25 / feature 1.5 / refactor 0.25).
• ai-contribution: 0 zero-weights AI-labeled PRs.
• emission_share and issue_discovery_share are unchanged.

Related Issues

N/A

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (scoring config)

Testing

• JSON validated; repo count and all other entries unchanged.
• Single-file change to gittensor/validator/weights/master_repositories.json;
  no code paths affected.

Checklist

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