fix(2meet-data-optimizer): refuse uninstall while data lives only in flat tables

- uninstall.php checks every site first and wp_die()s (keeping tables,
  options and plugin files) on aeav_only modes, misc rows, or zone
  modules past cutover; a failed bootstrap also refuses
- Multisite now checks and cleans every site: network activation is always
  false at uninstall, so only the main site was being cleaned before
- Drop the inline fallback DROP loop, unreachable now that a missing
  helper refuses instead

Verify: UninstallGuardTest (8 tests incl. running uninstall.php single and
  multisite); unit 602 OK, integration 429 OK
PR: PR-008

includes/class-tmdo-installer.php

@@ -297,6 +297,58 @@ class TMDO_Installer {
 		update_option( self::MISC_BUCKET_DEFAULT_FLAG, '1', true );
 	}
 
+	/**
+	 * Reasons this site's wpdo_* tables cannot be dropped yet; empty means safe.
+	 *
+	 * Reads the site's own options rather than Mode_Manager / Feature_Flags,
+	 * whose per-request caches do not follow switch_to_blog() during uninstall.
+	 *
+	 * @return string[]
+	 */
+	public static function uninstall_blockers(): array {
+		global $wpdb;
+		$blockers = array();
+
+		$modes = get_option( 'wpdo_bridge_modes', array() );
+		foreach ( is_array( $modes ) ? $modes : array() as $entity => $mode ) {
+			if ( 'aeav_only' === $mode ) {
+				$blockers[] = sprintf( '%1$s 的 bridge 模式是 aeav_only：資料只存在 wpdo_%1$s_* 扁平表。', $entity );
+			}
+		}
+
+		foreach ( array( 'wpdo_term_misc', 'wpdo_comment_misc' ) as $name ) {
+			if ( self::table_has_rows( $wpdb->prefix . $name ) ) {
+				$blockers[] = sprintf( '%s 有資料：這些 term / comment meta 只存在 misc 表。', $name );
+			}
+		}
+
+		$features = get_option( 'wpdo_features', array() );
+		foreach ( TMDO_Feature_Flags::ZONE_MODULES as $module ) {
+			$state = is_array( $features ) ? ( $features[ $module ] ?? 'idle' ) : 'idle';
+			if ( in_array( $state, array( 'cleanup', 'complete' ), true ) ) {
+				$blockers[] = sprintf( '區域模組 %1$s 處於 %2$s：讀取已改走 wpdo_* 表。', $module, $state );
+			}
+		}
+
+		return $blockers;
+	}
+
+	/**
+	 * Whether a table exists and holds at least one row.
+	 *
+	 * @param string $table Full table name.
+	 * @return bool
+	 */
+	private static function table_has_rows( string $table ): bool {
+		global $wpdb;
+		// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching,WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+		if ( $table !== $wpdb->get_var( $wpdb->prepare( 'SHOW TABLES LIKE %s', $wpdb->esc_like( $table ) ) ) ) {
+			return false;
+		}
+		return null !== $wpdb->get_var( "SELECT 1 FROM `{$table}` LIMIT 1" );
+		// phpcs:enable
+	}
+
 	// ── v2.0.0 entity + audit + shadow_diffs schema (PR-2) ─────────────────
 	// These tables are installed only when v2.0.0 upgrade runs (PR-7).
 	// install_v2_tables() is idempotent; safe to call multiple times.