refactor: replace route name with from/to endpoint labels

Route identity is now a (from_label, to_label) composite unique pair
instead of a single name column.  The three route migrations (create
tables, add reversible, replace name) are collapsed into one clean
migration since the feature hasn't shipped yet — 8f2a3c4d5e6f creates
all five tables with from_label/to_label + reversible from the start,
no intermediate steps.

Engine: recent_matches now returns the sliced subpath between the
matched endpoints, not the full path.  Diagnosis text moved to a hover
tooltip on the quality badge.  Cards sorted by from_label.  Seed YAML
switched to a list format with from/to keys; upsert by (from_label,
to_label).  Plan/tasks docs updated to present the final schema.

example/seed/routes.yaml

@@ -1,26 +1,30 @@
 # Routes seed file — route health monitoring definitions
 #
 # Loaded by `meshcore-hub seed` (and the compose `seed` profile).
-# Keyed by route name; each entry holds the route's knobs plus an ordered
-# `path` of node public_keys (>= 2, distinct) and optionally an `observers`
-# list of public_keys.
+# A list under the top-level `routes:` key. Each entry has `from`/`to`
+# endpoint labels, the route's knobs, and an ordered `path` of node
+# public_keys (>= 2, distinct) plus an optional `observers` list of
+# public_keys.
 #
-# Path nodes must already exist in the database (create them via
-# node_tags.yaml or let the collector discover them). Observer nodes that
-# don't exist yet are skipped with a warning (not an error).
+# Entries are upserted by the (from, to) label pair. Path nodes must
+# already exist in the database (create them via node_tags.yaml or let
+# the collector discover them). Observer nodes that don't exist yet are
+# skipped with a warning (not an error).
 
-Ipswich ↔ Norwich:
-  description: A140 corridor route
-  visibility: community
-  match_width: 1
-  window_hours: 24
-  packet_count_threshold: 3
-  # degraded_threshold: 10      # optional; omit/null = 2x threshold
-  # max_hop_span: 8             # optional; omit/null = unlimited
-  enabled: true
-  reversible: true                # match both directions (A->B and B->A)
-  path:
-    - a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2
-    - 9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b
-  # observers:                   # optional; omit/empty = all observers
-  #   - 0102030405060102030405060102030405060102030405060102030405060102
+routes:
+  - from: Ipswich
+    to: Norwich
+    description: A140 corridor route
+    visibility: community
+    match_width: 1
+    window_hours: 24
+    packet_count_threshold: 3
+    # degraded_threshold: 10      # optional; omit/null = 2x threshold
+    # max_hop_span: 8             # optional; omit/null = unlimited
+    enabled: true
+    reversible: true                # match both directions (A->B and B->A)
+    path:
+      - a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2
+      - 9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b7c6d5e4f9a8b
+    # observers:                   # optional; omit/empty = all observers
+    #   - 0102030405060102030405060102030405060102030405060102030405060102