Re-coarsen RU-ARK Arctic-coast band into RU-PEO + RU-YAM (#41)

#41: re-partition the RU-ARK mainland's 28-part lat>=68 Arctic-coast band
into two new regions via a new turf-free, idempotent pipeline stage
scripts/split-arkhangel-band.mjs (npm run split:regions:band), mirroring the
#31 split:

- RU-PEO (Pechora, 13 parts, ~37,678 km2) -> key pechora-qwhs
- RU-YAM (Yamal, 15 parts, ~51,722 km2) -> key yamal-gosw
- RU-ARK keeps its id/name/key arkhangel-sk-lhbk (ownership-safe); the 5-part
  lat<68 core (~305,229 km2) stays RU-ARK.

Pure re-partition: no geometry moved (byte-identical union). The two new
features are inserted immediately after RU-ARK-SZ. Manifests regenerated with
the real scripts (1,798 -> 1,800 keys + adjacency; adjacency pairs 4,471 ->
4,473). Fixed-point dataset unchanged except feature count (11,794 parts /
11,795 rings / 164,801 verts / 1 KZ-KZY hole). Four dataset/manifest tests
updated (RUS 82 -> 84 sub-regions). Version 0.25.0 -> 0.26.0.

Fixes #41

public/region-adjacency.json

@@ -887,7 +887,6 @@
     "komi-eoeh",
     "murmansk-etas",
     "nenets-qyga",
-    "severnaya-zemlya-awqp",
     "vologda-ynvr"
   ],
   "artigas-stkw": [
@@ -7588,6 +7587,7 @@
   "nenets-qyga": [
     "arkhangel-sk-lhbk",
     "komi-eoeh",
+    "pechora-qwhs",
     "yamal-nenets-aqsx"
   ],
   "neuquen-yvne": [
@@ -8750,6 +8750,10 @@
     "soriano-ixbv",
     "tacuarembo-yekg"
   ],
+  "pechora-qwhs": [
+    "nenets-qyga",
+    "yamal-gosw"
+  ],
   "peloponnisos-wqyw": [
     "dytiki-ellada-mlyj",
     "sterea-ellada-inyu"
@@ -10013,7 +10017,7 @@
     "skikda-odba"
   ],
   "severnaya-zemlya-awqp": [
-    "arkhangel-sk-lhbk"
+    "yamal-gosw"
   ],
   "sevilla-oxma": [
     "badajoz-ciwt",
@@ -12165,6 +12169,10 @@
     "iwate-uvfz",
     "niigata-idhx"
   ],
+  "yamal-gosw": [
+    "pechora-qwhs",
+    "severnaya-zemlya-awqp"
+  ],
   "yamal-nenets-aqsx": [
     "khanty-mansiy-tkto",
     "komi-eoeh",

public/region-keys.json

@@ -1307,6 +1307,8 @@
   "RU-ARK": "arkhangel-sk-lhbk",
   "RU-ARK-NE": "new-earth-eikt",
   "RU-ARK-SZ": "severnaya-zemlya-awqp",
+  "RU-PEO": "pechora-qwhs",
+  "RU-YAM": "yamal-gosw",
   "RU-AST": "astrakhan-anec",
   "RU-BA": "bashkortostan-uovk",
   "RU-BEL": "belgorod-wxjk",