realm: Replace occurrences of uri with url in templates.

[Vector73]

This PR is extracted from #29959 and reorganized to replace occurrences of URI with URL in:

• send_email.py, email templates and some other related files
• context_processors.py file and related templates

Screenshots and screen captures:

Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.

[Vector73]

I have manually tested some of the updated templates for both commits.

[timabbott]

I addressed the translation tests by:

• Updating the locale data to still have a translation for that email.
• Made sure Transifex has the translation updates so this doesn't break when we next sync from there.

With those changes, looks good, merged, thanks @Vector73!

[timabbott]

Fixed the tests properly this time, including a PROVISION_VERSION bump because we need compilemessages to have been run with the right strings.