android: show password validation feedback

[ZenulAbidin]

What changed

• show an inline warning when a new password is shorter than six characters
• show an inline warning when the confirmation does not match
• reuse one minimum-length value for both feedback and button validation

Why

The Android password dialog already prevented submission of passwords shorter than six characters, but the requirement was only encoded in the disabled OK button. Users were not told why the password could not be accepted.

This makes the existing validation visible without changing the password policy.

Fixes #8497.

Validation

• existing QML test suite: 8 passed
• headless state checks against the real PasswordDialog component, including short, mismatched, valid, and non-confirmation modes
• repeated the component checks against an isolated, non-editable install built from the source distribution
• git diff --check