Resolve Mastodon boosts to the original post before building responses - #743

Reeder for Mac failed to refresh or crashed when Friends returned a local boost wrapping another boost. Friends now resolves the boost target to the original post before constructing the Mastodon status, preserving the local boost's ID, account and timestamp and the original author's content and attachments. Cyclic or invalid targets are skipped. Friends remains authoritative for boost construction; EMA no longer needs to flatten nested boosts during JSON serialization.

This is the source fix identified through incremental Reeder debugging; the accompanying EMA image metadata correction is tracked in akirk/enable-mastodon-apps#355. A regression test exercises a multi-level boost before serialization.

Validation:

• User verified that the final source-based media and boost fixes load successfully in Reeder for Mac.
• Read-only wp --url=alex.kirk.at eval invoking Friends\Enable_Mastodon_Apps::mastodon_api_account_statuses: all 18 prepared boosts have zero nested boosts before serialization.
• Live GET /api/v1/accounts/2/statuses?exclude_replies=1&limit=40: 35 statuses, zero nested boosts with EMA's status serializer restored.
• PHP syntax checks for both changed files and targeted PHPCS passed.
• composer check-cs ran; it reported duplicate-class warnings from an existing .claude/worktrees/show-likes-received checkout. Targeted vendor/bin/phpcs --standard=../friends/phpcs.xml ../friends/integrations/class-enable-mastodon-apps.php ../friends/tests/test-only-ema.php --report=summary passed from the EMA workspace.
• Local PHPUnit could not start because the WordPress test library is missing. CI pending.

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