feat: add account deletion feature (#85)

* feat: add account deletion feature

- Add DELETE /auth/me endpoint to delete user account and all data
- Add deleteAccount() method to AuthContext
- Add Delete Account button with confirmation modal in UserProfile
- Add danger zone styling (.btn-danger, .profile-danger-zone)
- Add i18n translations for EN and DE
- Add backend tests for account deletion endpoint
- Add timeout settings to frontend vitest.config.ts
- Reduce CI timeout for frontend tests (10min -> 5min)

* fix: improve delete account section layout

- Make profile modal scrollable with max-height
- Add proper horizontal margin to danger zone
- Align delete section with form content

* fix: use ConfirmModal component for delete account dialog

- Replace inline modal with existing ConfirmModal component
- Ensures consistent button styling across all modals
- Add UI consistency rule to AGENTS.md and copilot-instructions.md

* fix: consistent styling for delete account section

- Remove warning text (users know what delete means)
- Remove border-bottom from danger zone title (section has border-top)
- Update copilot-instructions and AGENTS.md with stricter UI consistency rules
- Remove unused deleteAccountHint i18n keys

* chore: remove pre-push test hook (CI handles tests)

Tests were running twice - in pre-push hook and GitHub CI.
Removing local pre-push tests since CI provides authoritative test results.
Use 'npm test' manually before pushing if you want local feedback.

.husky/pre-push

@@ -1,31 +0,0 @@
-#!/bin/sh
-
-# Get the directory where the script is located
-SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-ROOT_DIR="$(dirname "$SCRIPT_DIR")"
-
-echo "Running backend tests before push..."
-cd "$ROOT_DIR/backend" && CI=true npm test
-
-if [ $? -ne 0 ]; then
-  echo "❌ Backend tests failed. Push aborted."
-  echo "Use 'git push --no-verify' to skip tests if needed."
-  exit 1
-fi
-
-echo "✅ Backend tests passed!"
-
-echo ""
-echo "Running frontend tests before push..."
-cd "$ROOT_DIR/frontend" && CI=true npm test
-
-if [ $? -ne 0 ]; then
-  echo "❌ Frontend tests failed. Push aborted."
-  echo "Use 'git push --no-verify' to skip tests if needed."
-  exit 1
-fi
-
-echo "✅ Frontend tests passed!"
-
-echo ""
-echo "✅ All tests passed! Pushing..."