Refactor toggleReaction to Return a Consistent Object

[Silent-Watcher]

Improvement: Standardize toggleReaction Return Value

Description:
Currently, toggleReaction returns different object shapes ({removed: true}, {createdReaction}, {createdOrUpdated}). Refactor it to always return a consistent shape: { action: 'added' | 'removed', doc: ReactionDoc | null }.

Acceptance Criteria:

• Return type is unified across both single and multi-reaction modes.
• action property clearly indicates what occurred.
• doc is null on removal, or the reaction document on add/update.
• All existing tests are updated to reflect the new return value.
• TypeScript definitions are updated.
• Add usage examples in docs