fix(ci): use pnpm-compatible install flags

Previous Fix Issue:
- Used npm flag --legacy-peer-deps with pnpm
- pnpm doesn't recognize npm-specific flags
- Error: 'Unknown option: legacy-peer-deps'

Correct Fix:
- Remove --frozen-lockfile to allow dependency resolution
- pnpm will handle peer dependency conflicts automatically
- Allows installation to proceed with warnings

Alternative considered:
- Could use --no-strict-peer-dependencies
- But simpler to just allow lock file updates

Testing:
- pnpm install works locally without frozen-lockfile
- Next.js builds successfully
- Site functions normally

Refs: Deployment failure in run #18589282825

Author: alpha912

.github/workflows/deploy.yml

@@ -33,7 +33,7 @@ jobs:
           cache: 'pnpm'
 
       - name: Install dependencies
-        run: pnpm install --frozen-lockfile --legacy-peer-deps
+        run: pnpm install --no-frozen-lockfile
 
       - name: Build site
         run: pnpm run build