feat(agent): make next-action recommendations repo-specific

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Problem

Agent recommendations can still be too generic. A miner should not just hear “pick one narrow change”; Gittensory should explain which repo, lane, work type, or cleanup action is most useful and why.

Desired behavior

Generate repo-specific next actions using contributor history, lane fit, queue pressure, duplicate risk, labels, language/path fit, maintainer-lane context, and prior outcome patterns.

Implementation notes

• Start in src/services/agent-orchestrator.ts, src/services/decision-pack.ts, and the reward/risk signal builders.
• Use existing stored contributor evidence and repo signal snapshots before adding new storage.
• Keep sorting deterministic.
• Separate maintainer-owned repos from normal contributor/miner evidence.
• Make recommendations concrete: repo, lane, action type, reason, blocker, and rerun condition.

Public/private boundaries

Private MCP/API output can explain scoreability, risk, and blocker impact. Public GitHub output must stay sanitized and avoid score estimates or private reviewability details.

Acceptance criteria

• Agent plan names specific repos and work types to pursue or avoid.
• Maintainer-owned repo history does not inflate normal contributor-lane evidence.
• Cleanup-first actions outrank new work when open PR pressure blocks scoreability.
• Direct-PR, issue-discovery, split, and maintainer lanes produce different reasoning.
• Recommendations are deterministic for the same input data.

Tests

• Direct-PR repo fixture.
• Issue-discovery-only repo fixture.
• Maintainer-lane fixture.
• High open-PR pressure fixture.
• Duplicate-risk fixture.
• Deterministic sorting regression.