adding sql schema for sqlite db, adding sqlite db to gitignore

.gitignore

@@ -11,6 +11,6 @@ __pycache__/
 *.pyc
 
 data-pipeline/kaikki-source-files/
-data-pipeline/db/pipeline.db
+data-pipeline/db/staging.db
 data-pipeline/.env
 .aider*

data-pipeline/db/schema.sql

@@ -0,0 +1,30 @@
+CREATE TABLE words (
+  id TEXT PRIMARY KEY,
+  headword TEXT NOT NULL,
+  language_code TEXT NOT NULL,
+  pos TEXT NOT NULL,
+  created_at TEXT DEFAULT (datetime('now')),
+  UNIQUE(headword, language_code, pos)
+);
+
+CREATE TABLE senses (
+  id TEXT PRIMARY KEY,
+  word_id TEXT NOT NULL REFERENCES words(id),
+  sense_index INTEGER NOT NULL DEFAULT 0,
+  difficulty TEXT NOT NULL,
+  definitions TEXT NOT NULL DEFAULT '[]',
+  examples TEXT NOT NULL DEFAULT '[]',
+  created_at TEXT DEFAULT (datetime('now')),
+  UNIQUE(word_id, sense_index)
+);
+
+CREATE TABLE translations (
+  id TEXT PRIMARY KEY,
+  sense_id TEXT NOT NULL REFERENCES senses(id),
+  target_language_code TEXT NOT NULL,
+  translation TEXT NOT NULL,
+  gender TEXT,
+  difficulty TEXT NOT NULL,
+  created_at TEXT DEFAULT (datetime('now')),
+  UNIQUE(sense_id, target_language_code, translation)
+);