add preferences and macOS packaging

migrations/20260724140000_create_preferences/down.sql

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+DROP TABLE preferences;

migrations/20260724140000_create_preferences/up.sql

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+CREATE TABLE preferences (
+    id INTEGER PRIMARY KEY NOT NULL CHECK (id = 1),
+    selected_model TEXT NOT NULL DEFAULT 'deepseek-v4-flash'
+        CHECK (selected_model IN ('deepseek-v4-flash', 'deepseek-v4-pro', 'glm-5.2')),
+    dflash_enabled BOOLEAN NOT NULL DEFAULT 0
+        CHECK (dflash_enabled IN (0, 1)),
+    idle_timeout_minutes INTEGER NOT NULL DEFAULT 10
+        CHECK (idle_timeout_minutes BETWEEN 1 AND 1440),
+    CHECK (dflash_enabled = 0 OR selected_model = 'deepseek-v4-flash')
+);
+
+INSERT INTO preferences (id) VALUES (1);