Add DB migrations and run them on startup

Enable sqlx "migrate" feature and add SQL migrations to create the
database schema: pg_trgm extension, sources, genres, authors, sequences,
books, junction tables, annotations, and supporting indexes

migrations/20260116092211_create_translations_table.sql

@@ -0,0 +1,14 @@
+-- Create translations junction table
+CREATE TABLE IF NOT EXISTS translations (
+    id SERIAL PRIMARY KEY,
+    position SMALLINT NOT NULL,
+    author INTEGER NOT NULL,
+    book INTEGER NOT NULL,
+    CONSTRAINT uc_translations_book_author UNIQUE (book, author),
+    CONSTRAINT fk_translations_authors_author_id FOREIGN KEY (author) REFERENCES authors(id) ON UPDATE CASCADE ON DELETE CASCADE,
+    CONSTRAINT fk_translations_books_book_id FOREIGN KEY (book) REFERENCES books(id) ON UPDATE CASCADE ON DELETE CASCADE
+);
+
+-- Create indexes for translations
+CREATE INDEX IF NOT EXISTS translations_author ON translations (author);
+CREATE INDEX IF NOT EXISTS translations_book ON translations (book);