feat(members): add admin view to search youth leaders by qualification

[chrisflav]

Summary

Implements #105 — search for youth leaders by qualification.

• Adds a new admin view at /kompass/members/member/search_youth_leaders/ (requires may_see_qualities permission) with filter fields for training categories and activity categories
• Results show all members who lead at least one group and match the selected filters (only trainings marked as passed are considered)
• Clicking "Contact" on any result opens a pre-filled contact form with subject and message body that can be edited before sending
• On submit, the email is sent to the selected youth leader with the triggering user set as reply-to and CC
• A link to the search page is shown on the members app index for users with may_see_qualities
• Tests added for all new views (permission checks, GET/POST flows)

Test plan

• Log in as superuser and navigate to Members → "Jugendleiter*innen nach Qualifikation suchen"
• Filter by training category and/or activity category; verify only matching youth leaders appear
• Click "Contact" on a result; verify the form is pre-filled with the youth leader's name
• Submit the form; verify the email is sent with the user in CC and reply-to
• Log in as a user without may_see_qualities; verify redirect on accessing the search URL
• Run make test-only — all new tests should pass

🤖 Generated with Claude Code

[github-actions]

📚 Documentation: https://chrisflav.github.io/kompass/feature/search-youth-leaders-by-qualification/

Docker Images:

• App: ghcr.io/chrisflav/kompass:pr-281
• Nginx: ghcr.io/chrisflav/kompass-nginx:pr-281

Add the awaiting-deployment label to deploy this PR to a staging server.

[chrisflav]

orchestra address review: Merge the latest upstream main into this branch. Also fix the missing translations added in this PR. Some of them are currently marked as fuzzy.