feat(routes): add per-route max_path_length cap

Adds a new nullable per-route knob that caps the total number of hops
in a candidate packet's path. Packets whose path exceeds the cap are
dropped from matching consideration entirely (before the subsequence
matcher runs), so over-long paths never count toward
packet_count_threshold. Complements the existing max_hop_span, which
only constrains the gap between the first and last matched configured
node.

- Route model + migration (additive, nullable, default null = unlimited)
- Threaded through matcher chain (_subsequence_indices early-return)
- All 5 evaluate/preview/recent_matches call sites updated
- API serializer/create/update/preview passthrough
- CLI seed YAML import (update + create paths)
- Frontend: distinct icons for span (<-o->) vs path-length (|<->|),
  always-rendered badges with infinity fallback, hover tooltips on
  every stats row item, i18n keys (en + nl)
- Tests: matcher unit tests (within/exceeds cap), API round-trip,
  CLI seed import

alembic/versions/20260720_1200_d307ee761a34_add_route_max_path_length.py

@@ -0,0 +1,40 @@
+"""add routes.max_path_length
+
+Revision ID: d307ee761a34
+Revises: 5e3b712ccf10
+Create Date: 2026-07-20 12:00:00.000000+00:00
+
+Adds a single nullable ``max_path_length`` column to ``routes``. The
+new knob caps the total number of hops in a candidate packet's full
+path; receptions whose path exceeds it are dropped from matching
+consideration entirely (before the subsequence matcher runs), so
+over-long paths never count toward ``packet_count_threshold``.  Complements
+the existing ``max_hop_span`` (which only constrains the gap between
+the first and last *matched* configured node).
+
+``null`` (the default) means unlimited and preserves the previous
+behaviour for every existing route, so this migration is additive and
+backwards-compatible with no data backfill.
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "d307ee761a34"
+down_revision: Union[str, None] = "5e3b712ccf10"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "routes",
+        sa.Column("max_path_length", sa.Integer(), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("routes", "max_path_length")