Add foregroundRegistrationMode enum to re-register all users on app foreground

[sfdctaka]

1. New enum PushNotificationForegroundRegistrationMode (before PushNotificationManagerError):

• .none — no re-registration on foreground
• .currentUser — re-register only the current user (preserves pre-14.0 behavior)
• .allUsers — re-register all logged-in users (new default)
• Doc comment calls out the Publisher/per-login billing concern explicitly

2. New property foregroundRegistrationMode: .allUsers replaces the old Bool
3. Deprecated shim for registerOnForeground: Bool — kept as a computed property that maps to the new enum, so existing apps don't break with a compiler error, just a deprecation warning
4. onAppWillEnterForeground — now switches on the mode: iterates UserAccountManager.shared.userAccounts() for .allUsers, falls back to current-user-only for .currentUser

[github-actions]

	Tests	Passed ✅	Skipped	Failed
AuthFlowTester UI Test Results all	1 ran	1 ✅

Test	Result
No test annotations available

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[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.32%. Comparing base (3cdaf5f) to head (5669051).
⚠️ Report is 5 commits behind head on dev.

Files with missing lines	Patch %	Lines
...ses/PushNotification/PushNotificationManager.swift	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #4030      +/-   ##
==========================================
- Coverage   70.46%   68.32%   -2.15%     
==========================================
  Files         245      245              
  Lines       21449    21457       +8     
==========================================
- Hits        15115    14661     -454     
- Misses       6334     6796     +462     

Components	Coverage Δ
Analytics	70.78% <ø> (ø)
Common	70.79% <ø> (-0.19%)	⬇️
Core	61.85% <75.00%> (-3.31%)	⬇️
SmartStore	73.44% <ø> (ø)
MobileSync	88.79% <ø> (ø)

Files with missing lines	Coverage Δ
...ses/PushNotification/PushNotificationManager.swift	83.54% <75.00%> (+1.48%)	⬆️

... and 26 files with indirect coverage changes

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[github-actions]

	Tests	Passed ☑️	Skipped	Failed ❌️
SalesforceSDKCore iOS ^26 Test Results	631 ran	630 ✅		1 ❌

Test	Result
SalesforceSDKCore iOS ^26 Test Results
SFUserAccountManagerTests.testUserAccountEncoding	❌ failure

• View SalesforceSDKCore iOS ^26 Test Results

[github-actions]

	Tests	Passed ✅	Skipped	Failed
SalesforceSDKCore iOS ^18 Test Results	631 ran	631 ✅

Test	Result
No test annotations available

• View SalesforceSDKCore iOS ^18 Test Results

[bbirman]

nice way to have a migration from the old to new property!

[wmathurin]

LGTM