[MergeDups] Add "Revert set" button to discard changes and reset to initial state

[Copilot]

• Add Redux action to reset merge state to initial state
• Store initial state snapshot when data is loaded
• Add helper function to detect if state has changed from initial
• Add "Revert set" button after "Defer" button in SaveDeferButtons component
• Disable "Revert set" button when no changes have been made
• Add confirmation dialog for revert action
• Add localization strings for button and dialog to en translation file
• Add tests for the new functionality
• Verify the implementation works correctly
• Address all review feedback
• Merge latest master branch

Latest Changes:

✅ Merged latest changes from master branch
✅ Resolved auto-merge conflict in MergeDupsReducer.test.ts
✅ All tests still passing after merge

Summary

All review feedback has been fully addressed and the branch is now up-to-date with master. The implementation:

• Resets only tree and audio.moves (the actual merge set state)
• Uses initialTree as a JSON string for efficient storage
• Button props are properly alphabetized with variant="contained"
• Tests use standard mockDispatch pattern for checking dispatched actions
• All 53 tests passing
• Linter passes with no warnings
• Build succeeds
• Up-to-date with master branch

Original prompt

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This section details on the original issue you should resolve

<issue_title>[MergeDups] Add "reset"/"start over" button</issue_title>
<issue_description>There's no undo button within the merge tool (too complex to track easily), so if the users (e.g.) deletes a sense then changes their mind, they have to either defer or exit the tool. Some sort of "reset" or "start over" button could be handy.

• Add a "Revert set" button right after the "Defer" button
• Disable the button when the current merge set's state has no changes from its initial state
• Clicking the button pops up a confirmation dialog
• Confirming resets the state for that merge set
• Add all strings to the en localization file</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3872

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This change is 

[Copilot]

@copilot Merge in master

Merged master branch successfully. All 53 tests still passing, linter passes, and build succeeds.

[imnasnainaec]

Disabled revert button (no active merge changes)

Enabled revert button (merge changes in progress)

Revert button tooltip

Revert cancel/confirm dialog

[imnasnainaec]

@imnasnainaec reviewed 2 of 8 files at r2, 1 of 4 files at r4, 1 of 3 files at r5, 1 of 2 files at r9, 1 of 1 files at r10, 2 of 2 files at r11, 1 of 1 files at r12, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @copilot)

[jasonleenaylor]

@jasonleenaylor reviewed 2 of 8 files at r2, 1 of 4 files at r4, 1 of 3 files at r5, 1 of 2 files at r9, 1 of 1 files at r10, 2 of 2 files at r11, 1 of 1 files at r12, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @copilot)