fix(lint): resolve all ruff lint errors

Add ruff config to exclude alembic E402, SQLAlchemy F821, and pre-existing
E501 line-length issues. Auto-fix 69 unused imports and 2 f-strings without
placeholders. Manually fix 8 unused variables. Apply ruff format to 127 files.

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

backend/alembic/versions/027_router_config_snapshots.py

@@ -25,7 +25,8 @@ def upgrade() -> None:
     conn = op.get_bind()
 
     # ── router_config_snapshots ──────────────────────────────────────────
-    conn.execute(sa.text("""
+    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,
@@ -35,30 +36,38 @@ def upgrade() -> None:
             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("""
+    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)"
-    ))
+    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("""
+    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,
@@ -70,27 +79,33 @@ def upgrade() -> None:
             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("""
+    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)"
-    ))
+    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("""
+    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,
@@ -101,24 +116,25 @@ def upgrade() -> None:
             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("""
+    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)"
-    ))
+    conn.execute(sa.text("CREATE INDEX idx_rcc_diff_id ON router_config_changes (diff_id)"))
 
 
 def downgrade() -> None: