feat: replace role=infra tag with adoption-based infrastructure detection

Replace the role=infra NodeTag convention with UserProfileNode adoption
as the canonical infrastructure indicator across map, Prometheus metrics,
and alerting. Renames is_infra to is_adopted, infra_center to
adopted_center. Map icons change to blue (adopted) / green (normal),
with all adoption UI gated on OIDC_ENABLED. Adds meshcore_nodes_adopted
gauge and Alembic migration to clean up obsolete tags.

alembic/versions/20260503_1800_remove_obsolete_node_tags.py

@@ -0,0 +1,25 @@
+"""remove obsolete role and member_id node tags
+
+Revision ID: 20260503_1800
+Revises: d7a9bbe85a9e
+Create Date: 2026-05-03 18:00:00.000000
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+
+revision: str = "20260503_1800"
+down_revision: Union[str, None] = "d7a9bbe85a9e"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.execute("DELETE FROM node_tags WHERE key = 'role' AND value = 'infra'")
+    op.execute("DELETE FROM node_tags WHERE key = 'member_id'")
+
+
+def downgrade() -> None:
+    pass