fix(2meet-data-optimizer): stop auto-activating entity bridge on install

- install() no longer switches the Hook Bus on or puts user/term/comment
  into dual_write; the now-unused maybe_autoactivate_entity_bridge() is gone
- Hook Bus and Mode_Manager defaults are off/disabled; sites with stored
  modes (incl. aeav_only) keep them since only unset keys use defaults
- Guard run_dbdelta()'s upgrade.php require like install_v2_tables() so
  install() can run under the integration test stub

Verify: InstallerV2Test::test_install_does_not_enable_entity_bridge,
  ModeManagerDefaultsTest; unit 602 OK, integration 421 OK
PR: PR-007

tests/unit/ModeManagerDefaultsTest.php

@@ -0,0 +1,50 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit test: TMDO_Mode_Manager defaults.
+ *
+ * A fresh install must not route any entity through the flat tables until an
+ * admin opts in; stored modes (e.g. aeav_only on live sites) must be kept as-is.
+ */
+class ModeManagerDefaultsTest extends TestCase {
+
+	protected function setUp(): void {
+		$GLOBALS['_wp_options'] = array();
+		TMDO_Mode_Manager::reset_cache();
+	}
+
+	protected function tearDown(): void {
+		TMDO_Mode_Manager::reset_cache();
+	}
+
+	public function test_all_entities_default_to_disabled(): void {
+		$this->assertSame(
+			array(
+				'post'    => TMDO_Mode_Manager::MODE_DISABLED,
+				'user'    => TMDO_Mode_Manager::MODE_DISABLED,
+				'term'    => TMDO_Mode_Manager::MODE_DISABLED,
+				'comment' => TMDO_Mode_Manager::MODE_DISABLED,
+			),
+			TMDO_Mode_Manager::all()
+		);
+	}
+
+	public function test_stored_modes_are_kept(): void {
+		update_option(
+			'wpdo_bridge_modes',
+			array(
+				'post' => 'aeav_only',
+				'user' => 'dual_write',
+			)
+		);
+
+		$modes = TMDO_Mode_Manager::all();
+
+		$this->assertSame( 'aeav_only', $modes['post'] );
+		$this->assertSame( 'dual_write', $modes['user'] );
+		$this->assertSame( TMDO_Mode_Manager::MODE_DISABLED, $modes['term'] );
+	}
+}