feat(06-01): migrate categories from emoji to Lucide icon field

- Rename emoji column to icon in schema, Zod schemas, and all services
- Add Drizzle migration with emoji-to-icon data conversion
- Update test helper, seed, and all test files for icon field
- All 87 tests pass with new icon-based schema

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

drizzle/meta/_journal.json

@@ -0,0 +1,20 @@
+{
+  "version": "7",
+  "dialect": "sqlite",
+  "entries": [
+    {
+      "idx": 0,
+      "version": "6",
+      "when": 1773589489626,
+      "tag": "0000_bitter_luckman",
+      "breakpoints": true
+    },
+    {
+      "idx": 1,
+      "version": "6",
+      "when": 1773593102000,
+      "tag": "0001_rename_emoji_to_icon",
+      "breakpoints": true
+    }
+  ]
+}