Add database schema

schema/current.sql

@@ -0,0 +1,19 @@
+CREATE TABLE settings (
+    key TEXT PRIMARY KEY,
+    value TEXT NOT NULL,
+    kind TEXT CHECK(kind IN ('int', 'string', 'bool', 'json', 'glob')) NOT NULL
+);
+
+INSERT INTO settings (key, value, kind) VALUES ('schema-version', '1', 'int');
+
+CREATE TABLE links (
+    id INTEGER PRIMARY KEY,
+    url TEXT NOT NULL,
+    title TEXT NOT NULL,
+    created_at TEXT NOT NULL,
+    updated_at TEXT,
+    is_private BOOLEAN NOT NULL DEFAULT 0
+);
+
+CREATE INDEX idx_links_created_at ON links(created_at);
+CREATE INDEX idx_links_url ON links(url);