perf: Batch snapshot collection to 1 SSH call per host (#130)

## Summary

Optimize `cf refresh` SSH calls from O(stacks) to O(hosts):
- Discovery: 1 SSH call per host (unchanged)
- Snapshots: 1 SSH call per host (was 1 per stack)

For 50 stacks across 4 hosts: 54 → 8 SSH calls.

## Changes

**Performance:**
- Use `docker ps` + `docker image inspect` instead of `docker compose images` per stack
- Batch snapshot collection by host in `collect_stacks_entries_on_host()`

**Architecture:**
- Add `build_discovery_results()` to `operations.py` (business logic)
- Keep progress bar wrapper in `cli/management.py` (presentation)
- Remove dead code: `discover_all_stacks_on_all_hosts()`, `collect_all_stacks_entries()`

.pre-commit-config.yaml

@@ -21,7 +21,7 @@ repos:
   - repo: https://github.com/astral-sh/ruff-pre-commit
     rev: v0.14.9
     hooks:
-      - id: ruff
+      - id: ruff-check
         args: [--fix]
       - id: ruff-format