feat: Hide the API key on settings page

[srinivasrk]

Description

Adds a secure-by-default API key input behavior in Settings UI by masking API keys initially and introducing an eye toggle (Eye/EyeOff) to reveal/hide on demand.
This keeps existing save/apply data flow unchanged while reducing accidental on-screen key exposure and aligns the interaction style with the channel config secret toggle pattern.

Related Issues

• Closes #N/A
• Related to #N/A

Module(s) Affected

• agents
• api
• config
• core
• knowledge
• logging
• services
• tools
• utils
• web (Frontend)
• docs (Documentation)
• scripts
• tests
• Other: ...

Checklist

• I have read and followed the contribution guidelines.
• My code follows the project's coding standards.
• I have run pre-commit run --all-files and fixed any issues.
• I have added relevant tests for my changes.
• I have updated the documentation (if necessary).
• My changes do not introduce any new security vulnerabilities.

Additional Notes

• UI-only change in web/app/(utility)/settings/page.tsx.
• API key field now uses password/text toggle with accessible labels (Show API key / Hide API key).
• Reveal state resets when switching service/profile to avoid unintended exposure.
• Verified no linter errors on the updated frontend file.