DNS single-source Phase 1 + decommission Tailscale fleet-wide

Phase 1 of the DNS-redundancy cleanup (keep NetBird, collapse toward one
zone) — the safe, mesh-independent half:

- Every homelab LXC now resolves via Technitium (192.168.8.2). Fixed 8
  boxes on a dead resolver (.180), the router (.1), or Tailscale MagicDNS
  (100.100.100.100): 101,102,104,105,106,114,119,126.
- Removed the redundant /etc/hosts auth/mcp/secrets overrides (Technitium
  returns identical-or-better answers); disabled hubris-hosts-override.
- Net effect: on-prem DNS (LXCs + household via Fritz!Box->Technitium) is
  now NetBird-independent, so dropping the managed zone later can't break
  on-LAN resolution. Phases 2-4 still pending.

Tailscale decommissioned (was legacy/being-phased-out):
- Removed from the 6 LXCs still running it (101,103,104,105,114,119):
  logout, disable tailscaled, apt purge, state cleared.
- inventory.yaml: dropped tailscale from accepted + all mesh blocks;
  regenerated hosts/*.yaml (also pruned orphan authentik/claudio-bot).
- Tightened secrets-issuance MESH_SUBNETS: removed the now-vestigial
  Tailscale CGNAT range 100.64.0.0/10.
- Updated narrative docs (mesh, dns, network, README, AGENTS,
  agent-enrollment, homelab-context, 105-apps, 107-dns).

Live infra changed on the fleet + Mac; this commit records the docs/inventory.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -35,7 +35,7 @@ See the full table in [`containers/index.md`](containers/index.md). Quick links:
 ### Cross-cutting infrastructure
 - [DNS — split-horizon](infrastructure/dns.md)
 - [Ingress — Caddy + VPS traefik](infrastructure/ingress.md)
-- [Mesh — Tailscale → Netbird migration](infrastructure/mesh.md)
+- [Mesh — Netbird overlay](infrastructure/mesh.md)
 - [Monitoring — Hermes health watchdog](infrastructure/monitoring.md)
 - [Media permissions — `media` GID 10000](infrastructure/media-permissions.md)
 - [SSH access](infrastructure/ssh-access.md)