[SPIKE] Foundation: Policy propagation progress tracking infrastructure

Problem

When policies are created/updated, propagation to target groups/projects happens asynchronously. Users have no visibility into this process and don't know when it's complete.

Solution

Build foundation infrastructure for policy propagation progress tracking that supports both regular policies and CSP scenarios.

Requirements (MoSCoW)

Must Have:

• Basic "propagation in progress" indicator
• Context awareness (regular policy vs CSP designation vs CSP policy updates)
• Minimal Redis/Sidekiq performance impact

Should Have:

• Progress percentage (e.g., "45% complete")
• Overall status (e.g., "15 of 30 projects updated")

Could Have:

• Detailed progress (which policy, which targets)
• Per-target status and failure tracking

Would Have:

• Time estimation
• Historical data
• Retry mechanisms

Implementation Phases

1. Phase 1: Lightweight Redis tracking + basic GQL subscription + simple UI indicator
2. Phase 2: Add completion counters + progress percentage
3. Phase 3: Detailed per-target tracking + granular UI
4. Phase 4: Advanced features (time estimation, analytics, retry)

Related Work

• PoC: !199270 (closed)
• CSP-specific extension: #559273 (closed)