feat: Auto-configure WAL mode on database open

- open() now automatically enables WAL mode for file-based databases
- Configures: journal_mode=WAL, synchronous=NORMAL, busy_timeout=5000ms
- Skips configuration for :memory: databases
- Added openRaw() for cases requiring default SQLite behavior
- Fixes: Database locked errors under concurrent load (Solo2 incident)

Benefits:
- Concurrent readers during writes
- 5s retry instead of immediate failure
- All projects using zcatsql benefit automatically

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/database.zig

@@ -59,6 +59,14 @@ pub const Database = struct {
     // ========================================================================
 
     /// Opens a database connection.
+    ///
+    /// For file-based databases, automatically configures for high availability:
+    /// - WAL mode (concurrent reads during writes)
+    /// - synchronous=NORMAL (balance of safety and speed)
+    /// - busy_timeout=5000ms (retry instead of immediate failure)
+    ///
+    /// For in-memory databases (`:memory:`), these settings are skipped.
+    /// Use `openRaw()` if you need the default SQLite behavior.
     pub fn open(path: [:0]const u8) Error!Self {
         var handle: ?*c.sqlite3 = null;
         const result = c.sqlite3_open(path.ptr, &handle);
@@ -70,6 +78,35 @@ pub const Database = struct {
             return resultToError(result);
         }
 
+        // Apply high-availability settings for file-based databases
+        // Skip for in-memory databases where WAL doesn't apply
+        if (!std.mem.eql(u8, path, ":memory:")) {
+            // WAL mode: allows concurrent readers during writes
+            _ = c.sqlite3_exec(handle, "PRAGMA journal_mode = WAL", null, null, null);
+            // NORMAL sync: good balance of durability and performance
+            _ = c.sqlite3_exec(handle, "PRAGMA synchronous = NORMAL", null, null, null);
+            // Wait 5 seconds instead of failing immediately when busy
+            _ = c.sqlite3_busy_timeout(handle, 5000);
+        }
+
+        return .{ .handle = handle };
+    }
+
+    /// Opens a database connection without automatic configuration.
+    ///
+    /// Unlike `open()`, this does not configure WAL mode or busy timeout.
+    /// Use this when you need full control over SQLite settings.
+    pub fn openRaw(path: [:0]const u8) Error!Self {
+        var handle: ?*c.sqlite3 = null;
+        const result = c.sqlite3_open(path.ptr, &handle);
+
+        if (result != c.SQLITE_OK) {
+            if (handle) |h| {
+                _ = c.sqlite3_close(h);
+            }
+            return resultToError(result);
+        }
+
         return .{ .handle = handle };
     }