feat(TRUEREF-0001): implement complete database schema and core data models

Define all SQLite tables via Drizzle ORM (repositories, repository_versions,
documents, snippets, snippet_embeddings, indexing_jobs, repository_configs,
settings), generate the initial migration, create FTS5 virtual table and
sync triggers in fts.sql, add shared TypeScript types in src/lib/types.ts,
and write 21 unit tests covering insertions, cascade deletes, FK constraints,
blob storage, JSON fields, and FTS5 trigger behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/server/db/migrations/meta/_journal.json

@@ -0,0 +1,13 @@
+{
+  "version": "7",
+  "dialect": "sqlite",
+  "entries": [
+    {
+      "idx": 0,
+      "version": "6",
+      "when": 1774196053634,
+      "tag": "0000_large_master_chief",
+      "breakpoints": true
+    }
+  ]
+}