fix(api): send invite email when creating Portal user (#145)

[b3lz3but]

Summary

• New users created via Portal invite or staff "Create User" were left with unusable passwords and no email sent — permanently locked out
• Both customer_users_create (API) and customer_create_user (staff view) now call the existing _send_welcome_email_secure() to send a password-reset invite
• Email failure is non-blocking: user is still created, staff gets a warning, API response includes invite_email_sent: false
• Added bilingual (RO/EN) welcome email templates (customers/emails/welcome_email.html + .txt)

Closes #145

Test plan

• test_create_user_success — verifies invite email is called and invite_email_sent: true in response
• test_create_user_invite_email_failure_still_succeeds — user created even if email fails
• test_create_user_sends_invite_email — staff view triggers email
• test_create_user_warns_on_email_failure — staff view shows warning on failure
• Full lint suite (7 phases) passing
• MyPy clean (468 source files)
• All pre-commit hooks passing

🤖 Generated with Claude Code

[b3lz3but]

@mostlyvirtual — this PR is ready for review.

[Copilot]

Pull request overview

Fixes a Portal onboarding gap where newly created customer users were left with unusable passwords and no invite/reset email, by triggering the existing secure welcome-email flow from both the API endpoint and the staff “Create User” view.

Changes:

• Send password-reset invite email after creating a customer user in customer_users_create (API) and customer_create_user (staff view).
• Return invite_email_sent in the API response and show a staff warning message if email sending fails.
• Add new customer welcome email templates (HTML + text) and tests covering success/failure scenarios.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
services/platform/apps/api/customers/views.py	Calls secure welcome-email sender and returns invite_email_sent in response.
services/platform/apps/customers/user_management_views.py	Calls secure welcome-email sender; warns staff when email fails.
services/platform/templates/customers/emails/welcome_email.txt	Adds plaintext welcome/invite template with reset link.
services/platform/templates/customers/emails/welcome_email.html	Adds HTML welcome/invite template with reset link/button.
services/platform/tests/api/test_customer_api.py	Adds API tests verifying email call + invite_email_sent behavior.
services/platform/tests/customers/test_user_management_views.py	Adds staff-view tests verifying email call + warning-on-failure behavior.

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[b3lz3but]

Review feedback addressed (68129f2)

1. Email expiry text — changed "3 days" → "2 hours" in both HTML and TXT templates to match PASSWORD_RESET_TIMEOUT=7200s.
2. request_ip audit logging — both call sites (API view + management view) now pass request_ip=get_safe_client_ip(request) to _send_welcome_email_secure. Tests updated.