feat: wild family complete — cave, mountain, river, lake, valley theme packs

Five wild-kernel themes, each 4 motifs:
  cave      dark · deep · echo · keeping        (cave geometry)
  mountain  ascent · cold · pass · weight       (cave)
  river     crossing · current · course · drowned  (fen)
  lake      stillness · mirror · sunken · rising   (fen)
  valley    ridges · shelter · bottom · weather (forest)

Two rendering fixes surfaced by the new claimants, both in skeleton.mjs:
  - `{conscript}'s` rendered "the climbers's"; conscripts are plural noun
    phrases, so fill() now collapses s's to s'.
  - claimants carrying their own article rendered "The The Grey"; named()
    only prefixes when one is absent.

All 16 themes validate; 39 tests pass. Module → 0.6.0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

foundry-module/module/core/content/index.json

@@ -13,6 +13,12 @@
       "geometry": "barrow",
       "motifs": 4
     },
+    {
+      "id": "cave",
+      "label": "Cave",
+      "geometry": "cave",
+      "motifs": 4
+    },
     {
       "id": "church",
       "label": "Church",
@@ -31,12 +37,24 @@
       "geometry": "forest",
       "motifs": 4
     },
+    {
+      "id": "lake",
+      "label": "Lake",
+      "geometry": "fen",
+      "motifs": 4
+    },
     {
       "id": "market",
       "label": "Market",
       "geometry": "village",
       "motifs": 4
     },
+    {
+      "id": "mountain",
+      "label": "Mountain",
+      "geometry": "cave",
+      "motifs": 4
+    },
     {
       "id": "palace",
       "label": "Palace",
@@ -49,6 +67,12 @@
       "geometry": "village",
       "motifs": 4
     },
+    {
+      "id": "river",
+      "label": "River",
+      "geometry": "fen",
+      "motifs": 4
+    },
     {
       "id": "temple",
       "label": "Temple",
@@ -61,6 +85,12 @@
       "geometry": "village",
       "motifs": 4
     },
+    {
+      "id": "valley",
+      "label": "Valley",
+      "geometry": "forest",
+      "motifs": 4
+    },
     {
       "id": "village",
       "label": "Village",