fix(deploy): Checkpoints — preserve STOPPED history, fix filter + placement

- Backend: rename deleteTerminalByAppAndEnvironment → deleteFailedByAppAndEnvironment.
  STOPPED rows were being wiped on every redeploy, so Checkpoints was always empty.
  Now only FAILED rows are pruned; STOPPED deployments are retained as restorable
  checkpoints (they still carry deployed_config_snapshot from their RUNNING window).
- UI filter: any deployment with a snapshot is a checkpoint (was RUNNING|DEGRADED only,
  which excluded the main case — the previous blue/green deployment now in STOPPED).
- UI placement: Checkpoints disclosure now renders inside IdentitySection, matching
  the design spec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -1,7 +1,7 @@
 <!-- gitnexus:start -->
 # GitNexus — Code Intelligence
 
-This project is indexed by GitNexus as **cameleer-server** (9095 symbols, 23495 relationships, 300 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
+This project is indexed by GitNexus as **cameleer-server** (9318 symbols, 23997 relationships, 300 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
 
 > If any GitNexus tool warns the index is stale, run `npx gitnexus analyze` in terminal first.