feat: support adding OTP to existing entries when scanning otpauth:// QR codes

[evilnull]

📝 Description

Previously, scanning an otpauth:// QR code via the system camera could only create a new entry. This change introduces an OTP search results page (OtpEntryResults) that searches for matching entries based on the issuer/label from the URI, allowing users to either add OTP to an existing entry or create a new one. When the selected entry already has OTP configured, a confirmation dialog asks whether to overwrite it.

🔗 Related Issue

#2791

🛠️ Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

✅ Checklist

Before submitting this PR, please confirm the following:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own (or any AI generated) code.
• I have added/updated tests that prove my fix is effective or that my feature works.
• All new and existing tests passed locally.
• I have commented my code, particularly in hard-to-understand areas.
• I have built the app locally, verified that it builds and tested the changes thoroughly.

---

📸 Screenshots/Videos (if applicable)