Replace loose equality with strict equality in SignInControl

[Copilot]

Addresses code review feedback from PR #1389 to use strict equality operators for type-safe comparisons.

Changes:

• Replaced all loose equality (==) with strict equality (===) in SignInControl.tsx
• Updated 7 comparisons against EmailSigninStep enum values
• Updated disabled prop comparison on email input field

Example:

// Before
if (emailSignInStep == EmailSigninStep.EnterEmail) {

// After  
if (emailSignInStep === EmailSigninStep.EnterEmail) {

---

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