feat(hemp): wild patches in plains/forest + chest seed injection

Two new ways to find hemp seeds without already having any:

1. Worldgen: minecraft:scatter_feature spawns 1-3 mature
   silverlabs:hemp_crop blocks on grass/dirt in plains/forest/birch/
   flower_forest biomes (~14% scatter chance per chunk surface pass).
2. Chest injection: 8% chance per chest first-open to plant 1-3 seeds
   in a random empty slot. Tracked per-chest via world dynamic property
   (rolling cap of 500 entries) so each chest only contributes once.

Bedrock has no loot-table merge mechanism so we can't add seeds to
vanilla village chests without losing their vanilla loot — script
injection sidesteps that and stays version-independent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hemp-addon/hemp_BP/feature_rules/hemp_patch_rule.json

@@ -0,0 +1,35 @@
+{
+  "format_version": "1.21.0",
+  "minecraft:feature_rules": {
+    "description": {
+      "identifier": "silverlabs:hemp_patch_rule",
+      "places_feature": "silverlabs:hemp_patch_feature"
+    },
+    "conditions": {
+      "placement_pass": "surface_pass",
+      "minecraft:biome_filter": [
+        {
+          "any_of": [
+            { "test": "has_biome_tag", "value": "plains" },
+            { "test": "has_biome_tag", "value": "forest" },
+            { "test": "has_biome_tag", "value": "birch" },
+            { "test": "has_biome_tag", "value": "flower_forest" }
+          ]
+        },
+        { "test": "has_biome_tag", "operator": "!=", "value": "monster" }
+      ]
+    },
+    "distribution": {
+      "iterations": 1,
+      "scatter_chance": 14,
+      "x": { "distribution": "uniform", "extent": [0, 16] },
+      "y": {
+        "distribution": "fixed_grid",
+        "extent": [0, 64],
+        "grid_offset": 0,
+        "step_size": 1
+      },
+      "z": { "distribution": "uniform", "extent": [0, 16] }
+    }
+  }
+}