feat: layer 4 invariants, mount checks, and deployment layer docs

- Rename biscayne-boot.yml → biscayne-prepare-agave.yml (layer 4)
- Document deployment layers and layer 4 invariants in playbook header
- Add zvol, ramdisk, rbind fstab management with stale entry cleanup
- Add kind node XFS verification (reads cluster-id from deployment)
- Add mount checks to health-check.yml (host mounts, kind visibility, propagation)
- Fix health-check discovery tasks with tags: [always] and non-fatal pod lookup
- Fix biscayne-redeploy.yml shell tasks missing executable: /bin/bash
- Add ansible_python_interpreter to inventory
- Update CLAUDE.md with deployment layers table and mount propagation notes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

inventory/biscayne.yml

@@ -4,6 +4,7 @@ all:
       ansible_host: biscayne.vaasl.io
       ansible_user: rix
       ansible_become: true
+      ansible_python_interpreter: /usr/bin/python3.12
 
       # DoubleZero identities
       dz_identity: 3Bw6v7EruQvTwoY79h2QjQCs2KBQFzSneBdYUbcXK1Tr