feat(traefik): keep each router's 4xx and 5xx responses by status code (#5711)

The scraper folded traefik_service_requests_total{code} into two shares and
dropped the code, so a problem couldn't say whether it was scanners (404), a
login wall (401/403) or the app down (502/503/504). Each scrape now stores the
responses per router and code that occurred (traefik_status_codes, migration
traefik_006), pruned with the router metrics and left out of backups (System
180 ruling: Traefik history is not backed up). A problem card lists its codes
over the last 15 minutes, most first, or says none occurred, or that codes
aren't recorded yet.

A counter series new since the previous scrape now counts from 0 instead of
being skipped: Traefik creates a router's 502 series at its first 502, so a
first burst of 5xx read as 0% until it happened again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/traefik/migrations/versions/traefik_006_status_codes.py

@@ -0,0 +1,40 @@
+"""Each router's 4xx and 5xx responses by status code
+
+The scraper folded traefik_service_requests_total{code} into a 4xx share and
+a 5xx share and dropped the code, so a problem couldn't say whether it was
+scanners probing (404), a login wall (401/403) or the app down (502/503/504)
+(#5711). One row per router, scrape and code that occurred; the page reads a
+router's codes over a time window, answered from the index alone.
+
+Revision ID: traefik_006_status_codes
+Revises: traefik_005_reload_at
+Create Date: 2026-10-14
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "traefik_006_status_codes"
+down_revision: Union[str, None] = "traefik_005_reload_at"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "traefik_status_codes",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column("router_name", sa.String(255), nullable=False),
+        sa.Column("scraped_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("code", sa.String(8), nullable=False),
+        sa.Column("count", sa.Integer, nullable=False),
+    )
+    op.create_index("ix_traefik_status_codes_router_scraped", "traefik_status_codes",
+                    ["router_name", "scraped_at"], postgresql_include=["code", "count"])
+    op.create_index("ix_traefik_status_codes_scraped", "traefik_status_codes", ["scraped_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_traefik_status_codes_scraped", "traefik_status_codes")
+    op.drop_index("ix_traefik_status_codes_router_scraped", "traefik_status_codes")
+    op.drop_table("traefik_status_codes")