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/models.py

@@ -67,3 +67,17 @@ class TraefikGlobalStat(Base):
     # traefik_config_last_reload_success gauge is that moment, not a 0/1 flag.
     config_last_reload_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
     process_memory_bytes: Mapped[float | None] = mapped_column(Float, nullable=True)
+
+
+class TraefikStatusCode(Base):
+    """How many responses a router answered with one 4xx or 5xx code in one
+    scrape interval (#5711): what lets a problem say whether it is scanners
+    probing (404), a login wall (401/403) or the app down (502/503/504).
+    Only codes that occurred are stored."""
+    __tablename__ = "traefik_status_codes"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=time_ordered_id)
+    router_name: Mapped[str] = mapped_column(String(255), nullable=False)
+    scraped_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    code: Mapped[str] = mapped_column(String(8), nullable=False)
+    count: Mapped[int] = mapped_column(Integer, nullable=False)