fix: Issue discovery Credits merged into Non-scoring Branches

[jonathanchang31]

Summary

Fixes issue-discovery branch-gate parity by exposing solving PR branch metadata in the miner issues API.
The inline solving_pr object now includes:

• base_ref
• head_ref
• head_repo_full_name
• default_branch

This lets gittensor apply the same merged-PR branch eligibility checks to issue discovery that it already applies to normal OSS PR scoring.

Related Issue

Fixes: #130

Change Type

• Bug fix
• API response shape enhancement
• Scoring-integrity fix
• New feature
• Refactor
• Documentation only
• Test-only change
• Breaking change

Real Behavior Proof

Seeded local Postgres with:

• repo default branch: main
• issue author: 111
• solving PR author: 222
• solving PR merged into: scratch-do-not-score
• issue state: CLOSED
• issue solved_by_pr: 7

Then queried:

curl -fsS \
  'http://127.0.0.1:6970/api/v1/miners/111/issues?since=2026-05-01T00:00:00.000Z'

Observed response proof:

{
  "issueCount": 1,
  "solvingPr": {
    "pr_number": 7,
    "base_ref": "scratch-do-not-score",
    "head_ref": "feature/solver",
    "head_repo_full_name": "codex-smoke/non-scoring-branch",
    "default_branch": "main"
  }
}

The mirror now exposes enough metadata for gittensor to identify the non-scoring branch case.

Checklist

• Analyzed das-github-mirror miner issue API path
• Analyzed connected gittensor issue-discovery and PR branch-gate logic
• Verified issue [Bug] Issue Discovery Credits Issues Solved by PRs Merged Into Non-Scoring Branches #130 behavior and required metadata
• Added base_ref to inline solving_pr
• Added head_ref to inline solving_pr
• Added head_repo_full_name to inline solving_pr
• Added default_branch to inline solving_pr
• Ran formatting check
• Ran lint
• Ran build
• Ran local runtime smoke test
• Verified API response includes the new fields
• Ran relevant gittensor compatibility tests
• Confirmed temporary smoke-test DB rows were cleaned up