fix: resolve template helper error for {{{ input }}} syntax (#6749)

[AlanNggg]

Description

Fixed "t.registerHelper is not a function" error when using {{{ input }}} in custom prompts by correctly importing the Handlebars default export.

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

1. Before the fix, custom prompts with {{{ input }}} failed with "t.registerHelper is not a function" error

2. After the fix, the prompts render correctly with proper input substitution

Tests

All existing tests in gui/src/components/mainInput/TipTapEditor/utils/renderPromptv1.test.ts pass

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Summary by cubic

Fixed Handlebars import to use the default export, resolving the “t.registerHelper is not a function” error and restoring correct rendering for custom prompts using {{{ input }}}.

^{Written for commit 253e43c. Summary will update automatically on new commits.}

[github-actions]

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[cubic-dev-ai]

No issues found across 1 file

[AlanNggg]

I have read the CLA Document and I hereby sign the CLA