worker+voice: per-conn context, store error hygiene, StateDir wiring, pipe leak

worker/server.go: dispatch now receives a per-connection context instead of
context.Background(), so handler cancellation propagates on conn close.

voice/server.go: same — per-conn context fed through safeDispatch into
HandlePushToTalk instead of context.Background().

store/reminders.go: propagate LastInsertId error.
store/nudges.go: propagate LastInsertId and RowsAffected errors.
store/tools.go: propagate RowsAffected error.

config/config.go: applyDefaults now respects StateDir when set, using it as
the base for empty DBPath/SocketPath instead of silently ignoring it.

phraser/llmphraser.go: close stderr pipe fd when cmd.Start() fails.

internal/config/config.go

@@ -256,11 +256,23 @@ func (c *Config) applyDefaults() {
 	if c.AutotuneInterval == 0 {
 		c.AutotuneInterval = Duration(DefaultAutotuneInterval)
 	}
-	if c.DBPath == "" {
-		c.DBPath = filepath.Join(defaultDataDir(), "maven.db")
-	}
-	if c.SocketPath == "" {
-		c.SocketPath = filepath.Join(defaultRuntimeDir(), "mavend.sock")
+	// StateDir — when set, use it as the base for both db and socket if their
+	// paths are still relative (empty). If StateDir is empty, fall back to the
+	// XDG-style defaults (data dir for db, runtime dir for socket).
+	if c.StateDir != "" {
+		if c.DBPath == "" {
+			c.DBPath = filepath.Join(c.StateDir, "maven.db")
+		}
+		if c.SocketPath == "" {
+			c.SocketPath = filepath.Join(c.StateDir, "mavend.sock")
+		}
+	} else {
+		if c.DBPath == "" {
+			c.DBPath = filepath.Join(defaultDataDir(), "maven.db")
+		}
+		if c.SocketPath == "" {
+			c.SocketPath = filepath.Join(defaultRuntimeDir(), "mavend.sock")
+		}
 	}
 }