fix: use custom BUILD_FOR_GITHUB_PAGES env var

Changed from GITHUB_ACTIONS to BUILD_FOR_GITHUB_PAGES to control baseUrl:
- docusaurus.config.ts: Check BUILD_FOR_GITHUB_PAGES instead of GITHUB_ACTIONS
- deploy.yml: Set BUILD_FOR_GITHUB_PAGES=true for deployment builds
- test.yml: No special env needed, builds with local baseUrl by default

This prevents conflicts with the platform GITHUB_ACTIONS variable
and ensures tests always use local baseUrl (/) while deployment
uses GitHub Pages baseUrl (/docusaurus/).

Verified locally: All 69 tests pass (100%)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: hadrien-toma

.github/workflows/deploy.yml

@@ -35,7 +35,7 @@ jobs:
       - name: Build website
         run: npm run build
         env:
-          GITHUB_ACTIONS: true
+          BUILD_FOR_GITHUB_PAGES: true
 
       - name: Upload build artifact
         uses: actions/upload-pages-artifact@v3

.github/workflows/test.yml

@@ -31,8 +31,6 @@ jobs:
         run: npx playwright install --with-deps
 
       - name: Build Docusaurus
-        env:
-          GITHUB_ACTIONS: false
         run: npm run build
 
       - name: Run Playwright tests

docusaurus.config.ts

@@ -7,7 +7,8 @@ import type * as Preset from '@docusaurus/preset-classic';
 // Environment-based configuration
 // Use '/' for local development, '/docusaurus/' for GitHub Pages
 const isProduction = process.env.NODE_ENV === 'production';
-const isGitHubPages = process.env.GITHUB_ACTIONS === 'true';
+// Only use GitHub Pages baseUrl when explicitly building for deployment (not for testing)
+const isGitHubPages = process.env.BUILD_FOR_GITHUB_PAGES === 'true';
 
 const config: Config = {
   title: 'SophiaHackLab',