Commit rest of changes

internal/storage/migrations/001_initial.sql

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+-- sessions table stores high-level chat session metadata.
+CREATE TABLE IF NOT EXISTS sessions (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    name TEXT NOT NULL,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    model_name TEXT NOT NULL,
+    summary TEXT
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_sessions_name ON sessions(name);
+
+-- messages table stores individual conversation messages linked to sessions.
+CREATE TABLE IF NOT EXISTS messages (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL,
+    role TEXT NOT NULL,
+    content TEXT NOT NULL,
+    token_count INTEGER,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY(session_id) REFERENCES sessions(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS idx_messages_session_created_at ON messages(session_id, created_at);
+
+-- models table tracks available models and usage metadata.
+CREATE TABLE IF NOT EXISTS models (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    name TEXT NOT NULL,
+    display_name TEXT,
+    provider TEXT,
+    is_default BOOLEAN NOT NULL DEFAULT 0,
+    last_used_at DATETIME
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_models_name ON models(name);