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/004_config_management.py

@@ -32,7 +32,8 @@ def upgrade() -> None:
     # Stores metadata for each backup run. The actual config content lives in
     # the tenant's bare git repository (GIT_STORE_PATH). This table provides
     # the timeline view and change tracking without duplicating file content.
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE TABLE IF NOT EXISTS config_backup_runs (
             id              UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
             device_id       UUID        NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
@@ -43,19 +44,24 @@ def upgrade() -> None:
             lines_removed   INT,
             created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
         )
-    """))
+    """)
+    )
 
-    conn.execute(sa.text(
-        "CREATE INDEX IF NOT EXISTS idx_config_backup_runs_device_created "
-        "ON config_backup_runs (device_id, created_at DESC)"
-    ))
+    conn.execute(
+        sa.text(
+            "CREATE INDEX IF NOT EXISTS idx_config_backup_runs_device_created "
+            "ON config_backup_runs (device_id, created_at DESC)"
+        )
+    )
 
     conn.execute(sa.text("ALTER TABLE config_backup_runs ENABLE ROW LEVEL SECURITY"))
 
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE POLICY tenant_isolation ON config_backup_runs
             USING (tenant_id::text = current_setting('app.current_tenant'))
-    """))
+    """)
+    )
 
     conn.execute(sa.text("GRANT SELECT, INSERT ON config_backup_runs TO app_user"))
     conn.execute(sa.text("GRANT SELECT ON config_backup_runs TO poller_user"))
@@ -68,7 +74,8 @@ def upgrade() -> None:
     # A per-device row with a specific device_id overrides the tenant default.
     # UNIQUE(tenant_id, device_id) allows one entry per (tenant, device) pair
     # where device_id NULL is the tenant-level default.
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE TABLE IF NOT EXISTS config_backup_schedules (
             id              UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
             tenant_id       UUID        NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
@@ -78,14 +85,17 @@ def upgrade() -> None:
             created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
             UNIQUE(tenant_id, device_id)
         )
-    """))
+    """)
+    )
 
     conn.execute(sa.text("ALTER TABLE config_backup_schedules ENABLE ROW LEVEL SECURITY"))
 
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE POLICY tenant_isolation ON config_backup_schedules
             USING (tenant_id::text = current_setting('app.current_tenant'))
-    """))
+    """)
+    )
 
     conn.execute(sa.text("GRANT SELECT, INSERT, UPDATE ON config_backup_schedules TO app_user"))
 
@@ -97,7 +107,8 @@ def upgrade() -> None:
     # startup handler checks for 'pending_verification' rows and either verifies
     # connectivity (clean up the RouterOS scheduler job) or marks as failed.
     # See Pitfall 6 in 04-RESEARCH.md.
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE TABLE IF NOT EXISTS config_push_operations (
             id                  UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
             device_id           UUID        NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
@@ -108,14 +119,17 @@ def upgrade() -> None:
             started_at          TIMESTAMPTZ NOT NULL DEFAULT NOW(),
             completed_at        TIMESTAMPTZ
         )
-    """))
+    """)
+    )
 
     conn.execute(sa.text("ALTER TABLE config_push_operations ENABLE ROW LEVEL SECURITY"))
 
-    conn.execute(sa.text("""
+    conn.execute(
+        sa.text("""
         CREATE POLICY tenant_isolation ON config_push_operations
             USING (tenant_id::text = current_setting('app.current_tenant'))
-    """))
+    """)
+    )
 
     conn.execute(sa.text("GRANT SELECT, INSERT, UPDATE ON config_push_operations TO app_user"))