EP-2612 - [Partial changes] Update cart header and empty cart message for clarity

[zweatshirt]

Description

Related Jira ticket

• We are trying to switch from the semantics of using a cart to giving gifts.
• Not all changes from the ticket were requested for the time being. If anything, this PR adds a bit more than what was requested by stakeholder(s) via email, but fulfills more of what the ticket they created asks for.

TODO:

• Update urls
• Update tracking and analytics references

Testing

• Find all instances in the application with 'Cart' terminology and ensure they've been replaced with 'Gift' or 'Selected Gift'

Checklist:

• I have given my PR a title with the format "EP-(JIRA#) (summary sentence max 80 chars)"
• I have applied the appropriate labels (Add the label "On Staging" to get the branch automatically merged into staging)
• I have requested a review from another person on the project
• I have checked that stage-branch-merger successfully merged my branch to staging or manually merged it myself
• I have tested my changes in staging for regular checkout
• I have tested my changes in staging for branded checkout

[Copilot]

Pull Request Overview

This PR updates user-facing terminology throughout the application, replacing "cart" language with "gifts" or "selected gifts" to better align with the giving/donation context. This improves clarity for users by using domain-specific language that better describes the donation selection process.

Key Changes:

• Replaced "cart" references with "gifts" or "selected gifts" in user-facing messages
• Updated button labels from "Add to Cart" to "Add to Gifts"
• Modified error messages to reference "gifts" instead of "cart"

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
userMatchModal.tpl.html	Simplified success message about resuming checkout
navCart.tpl.html	Updated empty state and error messages to use "gifts" terminology
failedVerificationModal.tpl.html	Changed error message to reference "gifts" instead of "cart"
enterAmounts.tpl.html	Updated button labels and error messages to use "gifts" terminology
productConfig.modal.tpl.html	Changed button labels from cart-related to gifts-related
main.tpl.html	Updated navigation link text from "Cart" to "Gifts"
step-1.tpl.html	Changed "Return to Cart" button to "Return to Selected Gifts"
checkout.tpl.html	Updated loading and error messages to reference "gifts"
cart-summary.tpl.html	Changed heading and button text to use "gifts" terminology
cart.tpl.html	Updated all user-facing text from cart to gifts terminology

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[Copilot]

Grammatical error: 'Your have' should be 'You have'.

Suggested change

	<p class="text-center mt-" translate>Your have no gifts selected</p>
	<p class="text-center mt-" translate>You have no gifts selected</p>

[Copilot]

Grammatical error: 'Your have' should be 'You have'.

Suggested change

	<p translate>Your have no selected gifts</p>
	<p translate>You have no selected gifts</p>

[Copilot]

The error message 'unable to be added to your gifts' is unclear. Consider using 'unable to be added' or 'could not be selected' to avoid the awkward 'added to your gifts' phrasing.

Suggested change

	There was an error adding some of your gifts. The ones below were
	unable to be added to your gifts.
	There was an error adding some of your gifts. The ones below could not be added.