Enable Blind Sign flow when fee estimation fails

[verificatorrus]

Context

In some cases (e.g. HTTP 500: too many iterations), fee emulation fails even though the transaction itself is valid and would be successfully executed on-chain.

Currently, when fee estimation fails, the UI completely blocks signing and sending the transaction, leaving the user with no way to proceed.

This PR addresses issue #536:
#536

What’s changed

• Introduced Blind Sign flow that allows users to proceed when fee estimation fails
• Added a global Security setting to explicitly enable/disable Blind Sign
• When enabled and fee estimation fails:
  • The user is shown a clear warning
  • The user must explicitly confirm sending without fee estimation
• Added a confirmation modal before signing without estimation
• Fully localized UI strings for all supported languages
• Integrated Blind Sign support for TonConnect transaction notifications

UX & Safety

• Blind Sign is disabled by default
• Enabling it requires explicit user confirmation with a risk warning
• Each transaction without estimation requires an additional confirmation step
• This keeps the default flow safe while still allowing advanced users to proceed in edge cases

Why this matters

Fee estimation failures should not fully block valid transactions.
This change improves reliability in edge cases while preserving user safety and control.

Fixes #536