fix: normalize username storage across all social auth providers

Every provider now stores username under the canonical 'username' key
in account data, matching BaseAuthProvider's new get_username() contract.

- Twitter: store username alongside screen_name
- Facebook: store page_name as username (posts as page)
- Threads: store page_name as username
- LinkedIn: store profile name as username
- Bluesky: override get_username() to read from config (app-password auth)
- Instagram: remove redundant get_username() override (base handles it)
- Reddit/Pinterest: already correct (username key or null)

This fixes the Studio Socials tab crash caused by get_platforms()
calling get_username() on providers that didn't implement it.

Author: chubes4

inc/Handlers/Bluesky/BlueskyAuth.php

@@ -33,6 +33,19 @@ public function is_authenticated(): bool {
 		! empty( $config['app_password'] );
 	}
 
+	/**
+	 * Get the Bluesky handle.
+	 *
+	 * Bluesky stores the handle in config (not account) because it uses
+	 * app-password auth rather than OAuth token exchange.
+	 *
+	 * @return string|null Handle or null
+	 */
+	public function get_username(): ?string {
+		$config = $this->get_config();
+		return ! empty( $config['username'] ) ? $config['username'] : null;
+	}
+
 	public function get_config_fields(): array {
 		return array(
 			'username'     => array(

inc/Handlers/Facebook/FacebookAuth.php

@@ -327,14 +327,17 @@ function ( $long_lived_token_data ) {
 					$user_profile_name = $profile_info['name'] ?? 'ErrorFetchingName';
 				}
 
+				$page_name = $page_credentials['name'] ?? '';
+
 				return array(
 					'user_access_token' => $access_token,
 					'page_access_token' => $page_credentials['access_token'],
 					'token_type'        => 'bearer',
 					'user_id'           => $user_profile_id,
+					'username'          => $page_name,
 					'user_name'         => $user_profile_name,
 					'page_id'           => $page_credentials['id'],
-					'page_name'         => $page_credentials['name'],
+					'page_name'         => $page_name,
 					'authenticated_at'  => time(),
 					'token_expires_at'  => $token_expires_at,
 				);

inc/Handlers/Instagram/InstagramAuth.php

@@ -116,18 +116,8 @@ public function get_user_id(): ?string {
 		return $account['user_id'];
 	}
 
-	/**
-	 * Get stored Instagram username
-	 *
-	 * @return string|null Username or null
-	 */
-	public function get_username(): ?string {
-		$account = $this->get_account();
-		if ( empty( $account ) || ! is_array( $account ) || empty( $account['username'] ) ) {
-			return null;
-		}
-		return $account['username'];
-	}
+	// get_username() is inherited from BaseAuthProvider.
+	// Instagram already stores username under the canonical 'username' key.
 
 	/**
 	 * Get authorization URL for Instagram OAuth

inc/Handlers/LinkedIn/LinkedInAuth.php

@@ -185,6 +185,7 @@ function ( $token_data ) {
 					'token_type'       => 'bearer',
 					'token_expires_at' => $expires_at,
 					'person_id'        => $profile['sub'] ?? '',
+					'username'         => $profile['name'] ?? 'Unknown',
 					'name'             => $profile['name'] ?? 'Unknown',
 					'email'            => $profile['email'] ?? '',
 					'picture'          => $profile['picture'] ?? '',

inc/Handlers/Threads/ThreadsAuth.php

@@ -169,11 +169,14 @@ function ( $long_lived_token_data ) {
 					);
 				}
 
+				$page_name = $posting_entity_info['name'] ?? 'Unknown Page/User';
+
 				return array(
 					'access_token'     => $access_token,
 					'token_type'       => 'bearer',
+					'username'         => $page_name,
 					'page_id'          => $posting_entity_info['id'],
-					'page_name'        => $posting_entity_info['name'] ?? 'Unknown Page/User',
+					'page_name'        => $page_name,
 					'authenticated_at' => time(),
 					'token_expires_at' => $token_expires_at,
 				);

inc/Handlers/Twitter/TwitterAuth.php

@@ -177,12 +177,15 @@ public function handle_oauth_callback() {
 			$api_key,
 			$api_secret,
 			function ( $access_token_data ) {
-				// Build account data from Twitter response
+				$screen_name = $access_token_data['screen_name'] ?? null;
+
+				// Build account data from Twitter response.
 				return array(
 					'access_token'        => $access_token_data['oauth_token'],
 					'access_token_secret' => $access_token_data['oauth_token_secret'],
 					'user_id'             => $access_token_data['user_id'] ?? null,
-					'screen_name'         => $access_token_data['screen_name'] ?? null,
+					'username'            => $screen_name,
+					'screen_name'         => $screen_name,
 					'last_verified_at'    => time(),
 				);
 			},