fix(teams): add /accept path to invitation email URL

[tturnerdev]

Summary

• The team invitation email links to /teams/{id}/invitations/{id} but the frontend accept page route is at /teams/{id}/invitations/{id}/accept
• Without the /accept suffix, clicking the link loads the team detail page (or redirects to /home if the user isn't a member), instead of showing the accept/decline UI

Test plan

• Invite a user to a team
• Open the invitation email in Mailpit
• Verify the URL ends with /accept
• Click the link — should show the accept/decline invitation page

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[tturnerdev]

PR created by AI; reviewed and verified by me.

Here's a screenshot of the invite email in Mailpit:

Example invite URL from screenshot:

http://localhost:8000/teams/019dd205-5ce4-7681-8235-198edf549ec9/invitations/019dd23a-8d1e-7351-a382-16ab3206abcd

Navigating to this URL resulted in either:

1. Already logged in: redirect to /home (http://localhost/home); or
2. Not logged in: redirect to to /login (http://localhost/home)

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Additionally, in my testing, when appending /accept to the URL, it does appear the URL redirected correctly, however, I ran into 403 errors (assuming due to the /teams/[id] route being permissioned).

This issue is addressed separately in #254