Fix search bar initially shows "No results found"

[Copilot]

Summary

Fixes #10645

When adding users to a project, the search bar incorrectly shows "No results found" when only 1 character is typed. The backend requires a minimum of 2 characters to return results.

Occurred changes and/or fixed issues

• SelectPrincipal.vue: Added minimum character check before calling search API
• When search string < 2 chars, displays "Type at least 2 characters to search" instead of "No results found"
• Added translation key cluster.memberRoles.addClusterMember.minCharacters

Technical notes summary

• Added hasSearchTooShort flag to track when search input is below threshold
• minSearchLength constant (2) matches backend requirement
• API call is skipped entirely when input too short, avoiding unnecessary requests

Areas or cases that should be tested

• Project Members → Add → type single character → should show "Type at least 2 characters to search"
• Type 2+ characters → should show search results or "No results found" if none match
• Clear search → should reset to default state
• Tested in Chrome; reviewer should test Firefox/Safari

Areas which could experience regressions

• SelectPrincipal component used in cluster member assignment
• Any other principal/user search dialogs using this component

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
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• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Search bar initially shows "No results found"</issue_title>
<issue_description><!--------- For bugs and general issues --------->
Setup

• Rancher version: 2.7-head

Describe the bug
When adding users to a project, the search bar doesn't show the matching results until the 2nd character is typed.

To Reproduce

1. Under Users & Authentication, create a new user (the kind of permissions are not relevant for this issue)
2. Create a project in a cluster
3. In the Members sessions, click Add
4. Type the name of an existing user
5. Observe the behavior of the search bar

Result
When adding users to a project, the search bar doesn't show the matching results until the 2nd character is typed. Also, the search engine shows the wrong message of "No results found"

Screen.Recording.2024-03-18.at.5.55.47.PM.mov

Expected Result
The search bar must show all matching results from the first character typed, and show the "No results found" message only when there are no matching results at all

</issue_description>

Comments on the Issue (you are @copilot in this section)

@nwmac I think the backend requires a minimum of 2 characters to return results, so we should handle that in the UI.

• Fixes Search bar initially shows "No results found" #10645

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[aalves08]

LGTM