Fix issues with new create wallet dialogue

[sbddesign]

With this PR, I aim to fix #151.

As @Rspigler noted in the issue:

1. When creating a new wallet, the UI offers an option to "encrypt wallet", which is misleading, because only private keys are encrypted and not other wallet data.
2. There are issues with the options for Disable Private Keys and Make Blank Wallet being disabled/enabled in ways that don't make sense.

Point number one is still an issue. However, as @vasild mentioned here, point number 2 is no longer happening as of 17072f7. They point out another inconsistency where:

• User chooses "Encrypt Wallet"
  • This disables "Disable Private Keys" in an unchecked state
• User chooses "Make Blank Wallet"
• Uses unchecks "Make Blank Wallet"
  • This enables "Disable Private Keys", allowing it to be checked

This PR fixes @Rspigler's point number one by changing the "Encrypt Wallet" tooltip to clarify that it encrypts the private key rather than the wallet. It also fixes @vasild's noted inconsistency where the checkbox becomes re-enabled.

Rationale

I considered for a moment that it might be more technically accurately to say "encrypt private key" instead of "encrypt wallet". However, I counted 27 instances of user-facing strings that describe encrypting the wallet. Users might be accustomed to the feature being called "encrypt wallet", so changing the text all across the app felt drastic, IMHO. Therefore, I thought we could simply provide some clarification in the tooltip that encrypting the wallet specifically means encrypting the private keys, but not other wallet metadata.

Testing

I successfully built the application with each commit of this PR, and I ran ctest --test-dir build to verify all the tests passed.

First PR

This is my first time opening a PR to Bitcoin Core. I've done my research on best practices, but I probably made errors. Happy to correct anything I may have missed.

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Concept ACK	ShauryaaSharma

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[luke-jr]

Seems like the opposite fix is also needed?

I feel like this whole logic needs to be rewritten...

[ShauryaaSharma]

Heey i was actually going through issue #151.
Saw that this pr was still open. Just wanted to see the approch you took.

Concept ACK on both fixes.

The wording approach is sensible, keeping the familiar "Encrypt Wallet" label while clarifying in the tooltip that it encrypts the private keys specifically (not all wallet metadata) is a good balance between accuracy and not disrupting the 27 other instances across the app.

On the checkbox fix: the blank_wallet_checkbox handler correctly gets !checked && !ui->encrypt_wallet_checkbox->isChecked(), but as luke-jr noted, the symmetric case is missing. The encrypt_wallet_checkbox toggled handler at line 31 has the same pattern:

ui->disable_privkeys_checkbox->setEnabled(!checked);

This causes an identical bug in the other direction, if blank_wallet_checkbox is checked, then encrypt_wallet_checkbox is toggled on and back off, disable_privkeys_checkbox incorrectly becomes re-enabled. The fix is symmetric:

ui->disable_privkeys_checkbox->setEnabled(!checked && !ui->blank_wallet_checkbox->isChecked());

Adding that one line alongside your existing fix would fully cover vasild's noted inconsistency in both directions.