fix: configure ccache after cache restore to prevent stale config

Same ordering bug as Conan profile (Session 8) - ccache config was being
created in workflow BEFORE cache restore, causing cached ccache.conf to
overwrite fresh configuration.

Changes:
- Build action: Add ccache config inputs (max_size, hash_dir, compiler_check)
- Build action: Configure ccache AFTER cache restore (overwrites cached config)
- Build action: Add "Show ccache config before build" step (debugging aid)
- Build action: Remove debug steps (past debugging phase)
- Build action: Remove ninja -v flag (past debugging phase)
- Nix workflow: Remove "Configure ccache" step (now handled in build action)
- macOS workflow: Remove "Configure ccache" step (now handled in build action)
- macOS workflow: Add missing stdlib and AWS credentials to build step
- Delete unused xahau-configure-ccache action (logic moved to build action)

Flow now matches Conan pattern:
1. Restore cache (includes potentially stale config)
2. Configure ccache (overwrites with fresh config: 2G max, hash_dir=true, compiler_check=content)
3. Show config (verification)
4. Build

This ensures fresh ccache configuration for each job, preventing issues
from cached config files with different settings.

.github/workflows/xahau-ga-macos.yml.disabled

@@ -78,14 +78,6 @@ jobs:
       - name: Install ccache
         run: brew install ccache
 
-      - name: Configure ccache
-        uses: ./.github/actions/xahau-configure-ccache
-        with:
-          max_size: 2G
-          hash_dir: true
-          compiler_check: content
-          is_main_branch: ${{ github.ref_name == env.MAIN_BRANCH_NAME }}
-
       - name: Check environment
         run: |
           echo "PATH:"
@@ -130,6 +122,9 @@ jobs:
           compiler-id: clang
           cache_version: ${{ env.CACHE_VERSION }}
           main_branch: ${{ env.MAIN_BRANCH_NAME }}
+          stdlib: libcxx
+          aws-access-key-id: ${{ secrets.XAHAUD_GITHUB_ACTIONS_CACHE_NIQ_AWS_KEY_ID }}
+          aws-secret-access-key: ${{ secrets.XAHAUD_GITHUB_ACTIONS_CACHE_NIQ_AWS_ACCESS_KEY }}
 
       - name: Test
         run: |

.github/workflows/xahau-ga-nix.yml

@@ -231,13 +231,6 @@ jobs:
           # Install Conan 2
           pip install --upgrade "conan>=2.0,<3"
 
-      - name: Configure ccache
-        uses: ./.github/actions/xahau-configure-ccache
-        with:
-          max_size: 2G
-          hash_dir: true
-          compiler_check: content
-
       - name: Check environment
         run: |
           echo "PATH:"