feat(01-01): add Alembic migration 027 for config snapshot tables with RLS

- Create router_config_snapshots table with Transit ciphertext storage
- Create router_config_diffs table with snapshot pair FK references
- Create router_config_changes table for parsed semantic changes
- Add RLS tenant isolation (ENABLE + FORCE + USING + WITH CHECK) on all 3
- Add GRANT SELECT/INSERT/DELETE to app_user on all 3
- Add performance indexes: device+collected_at, device+hash, snapshot pair, diff_id

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

backend/alembic/versions/027_router_config_snapshots.py

@@ -0,0 +1,129 @@
+"""Add router config snapshot, diff, and change tables.
+
+Creates three tables for config snapshot storage:
+- router_config_snapshots: point-in-time config captures (Transit-encrypted)
+- router_config_diffs: unified diffs between consecutive snapshots
+- router_config_changes: parsed semantic changes from diffs
+
+All tables have RLS tenant isolation and performance indexes.
+
+Revision ID: 027
+Revises: 026
+Create Date: 2026-03-12
+"""
+
+revision = "027"
+down_revision = "026"
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # ── router_config_snapshots ──────────────────────────────────────────
+    conn.execute(sa.text("""
+        CREATE TABLE router_config_snapshots (
+            id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+            device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+            tenant_id UUID NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+            config_text TEXT NOT NULL,
+            sha256_hash VARCHAR(64) NOT NULL,
+            collected_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+            created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        )
+    """))
+
+    # RLS
+    conn.execute(sa.text("ALTER TABLE router_config_snapshots ENABLE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("ALTER TABLE router_config_snapshots FORCE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("""
+        CREATE POLICY tenant_isolation ON router_config_snapshots
+            USING (tenant_id::text = current_setting('app.current_tenant', true))
+            WITH CHECK (tenant_id::text = current_setting('app.current_tenant', true))
+    """))
+
+    # Grants
+    conn.execute(sa.text("GRANT SELECT, INSERT, DELETE ON router_config_snapshots TO app_user"))
+
+    # Indexes
+    conn.execute(sa.text(
+        "CREATE INDEX idx_rcs_device_collected ON router_config_snapshots (device_id, collected_at DESC)"
+    ))
+    conn.execute(sa.text(
+        "CREATE INDEX idx_rcs_device_hash ON router_config_snapshots (device_id, sha256_hash)"
+    ))
+
+    # ── router_config_diffs ──────────────────────────────────────────────
+    conn.execute(sa.text("""
+        CREATE TABLE router_config_diffs (
+            id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+            device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+            tenant_id UUID NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+            old_snapshot_id UUID NOT NULL REFERENCES router_config_snapshots(id) ON DELETE CASCADE,
+            new_snapshot_id UUID NOT NULL REFERENCES router_config_snapshots(id) ON DELETE CASCADE,
+            diff_text TEXT NOT NULL,
+            lines_added INT NOT NULL DEFAULT 0,
+            lines_removed INT NOT NULL DEFAULT 0,
+            created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        )
+    """))
+
+    # RLS
+    conn.execute(sa.text("ALTER TABLE router_config_diffs ENABLE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("ALTER TABLE router_config_diffs FORCE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("""
+        CREATE POLICY tenant_isolation ON router_config_diffs
+            USING (tenant_id::text = current_setting('app.current_tenant', true))
+            WITH CHECK (tenant_id::text = current_setting('app.current_tenant', true))
+    """))
+
+    # Grants
+    conn.execute(sa.text("GRANT SELECT, INSERT, DELETE ON router_config_diffs TO app_user"))
+
+    # Indexes
+    conn.execute(sa.text(
+        "CREATE UNIQUE INDEX idx_rcd_snapshot_pair ON router_config_diffs (old_snapshot_id, new_snapshot_id)"
+    ))
+
+    # ── router_config_changes ────────────────────────────────────────────
+    conn.execute(sa.text("""
+        CREATE TABLE router_config_changes (
+            id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+            diff_id UUID NOT NULL REFERENCES router_config_diffs(id) ON DELETE CASCADE,
+            device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+            tenant_id UUID NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+            component TEXT NOT NULL,
+            summary TEXT NOT NULL,
+            raw_line TEXT,
+            created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        )
+    """))
+
+    # RLS
+    conn.execute(sa.text("ALTER TABLE router_config_changes ENABLE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("ALTER TABLE router_config_changes FORCE ROW LEVEL SECURITY"))
+    conn.execute(sa.text("""
+        CREATE POLICY tenant_isolation ON router_config_changes
+            USING (tenant_id::text = current_setting('app.current_tenant', true))
+            WITH CHECK (tenant_id::text = current_setting('app.current_tenant', true))
+    """))
+
+    # Grants
+    conn.execute(sa.text("GRANT SELECT, INSERT, DELETE ON router_config_changes TO app_user"))
+
+    # Indexes
+    conn.execute(sa.text(
+        "CREATE INDEX idx_rcc_diff_id ON router_config_changes (diff_id)"
+    ))
+
+
+def downgrade() -> None:
+    conn = op.get_bind()
+
+    conn.execute(sa.text("DROP TABLE IF EXISTS router_config_changes"))
+    conn.execute(sa.text("DROP TABLE IF EXISTS router_config_diffs"))
+    conn.execute(sa.text("DROP TABLE IF EXISTS router_config_snapshots"))