[Task]: Add governance query store contracts

[rian-be]

Summary

Introduce query contracts for governance requests, approvals, and decisions.

Goal

Make governance runtime operationally queryable instead of only retrievable by direct request lookup.

Problem

Governance runtime is becoming execution-aware and persistence-aware, but the read side is still too narrow. Once requests, approvals, decisions, and execution outcomes accumulate, users need to answer questions such as:

• what approvals are pending for a given actor?
• what requests touched this state or category?
• what recent stale resolutions or rejections occurred?
• what high-risk requests are still open?

That requires a dedicated query contract rather than ad hoc storage access.

Scope

• Introduce IMutationRequestQueryStore or equivalent query contract
• Query pending approvals by actor, group, role, or request category
• Query requests by stateId, category, tags, metadata, and blast radius
• Query recent request decisions, approval actions, stale resolutions, and execution outcomes
• Define storage-agnostic query contracts before provider-specific implementations

Design Expectations

• Query contracts should stay storage-agnostic.
• The read side should distinguish request state, approval state, and execution outcome clearly.
• Query filters should support both operational usage and later reporting surfaces.
• The model should not force consumers to reconstruct workflows manually from low-level store access.

Acceptance Criteria

• Governance query contracts cover request, approval, and decision scenarios
• Query model supports both operational and reporting-style retrieval
• Contracts are independent from concrete persistence providers
• Example usage or docs show how the query surface is meant to be consumed

Non-Goals

• This issue does not implement EF Core or PostgreSQL providers
• This issue does not define dashboards or UI surfaces
• This issue does not redesign the write-side storage contract

Notes

Persistence without queryability is only a storage layer. This issue is about the read side of governance data.