remove hosts/ directory — single source of truth is inventory.yaml

- Delete cmd/oikos/build_hosts.go (generator no longer needed)
- Remove build-hosts subcommand from main.go
- Fix oikos homelab whoami: read from inventory.yaml instead of hosts/
- Update bootstrap.sh: identity check uses inventory.yaml
- Remove all 27 generated hosts/*.yaml files
- Update AGENTS.md and OIKOS.md to reference inventory.yaml only

bootstrap.sh

@@ -314,10 +314,10 @@ else
 fi
 
 # -------- identity check --------
-HOST_YAML="$CLONE_DIR/hosts/$HNAME.yaml"
-if [ ! -f "$HOST_YAML" ]; then
+INVENTORY="$CLONE_DIR/inventory.yaml"
+if [ ! -f "$INVENTORY" ] || ! grep -q "^  $HNAME:" "$INVENTORY" 2>/dev/null; then
     cat >&2 <<EOF
-[bootstrap] no hosts/$HNAME.yaml in the repo.
+[bootstrap] no entry for '$HNAME' in inventory.yaml.
 This client has not been enrolled yet. From any existing client, run:
 
     homelab client add $HNAME
@@ -669,7 +669,7 @@ cat <<EOF
 
 [bootstrap] done.
 
-Identity:     $CLONE_DIR/hosts/$HNAME.yaml
+Identity:     $CLONE_DIR/inventory.yaml
 Sync:         5-minute interval ($([ "$OS" = "Darwin" ] && echo launchd || echo systemd))
 Manual pull:  homelab sync     (or 'systemctl start homelab-context-sync' / 'launchctl kickstart')
 CLI:          /usr/local/bin/homelab     (try 'homelab whoami')