refactor: move Conan profile creation after cache restore

PROBLEM: Profile was created before cache restore, then immediately
overwritten by cached profile. This meant we were using a potentially
stale cached profile instead of fresh configuration.

SOLUTION: Move profile creation into dependencies action after restore
- Dependencies action now takes compiler params as inputs
- Profile created AFTER cache restore (overwrites any cached profile)
- Ensures fresh profile with correct compiler settings for each job

CHANGES:
- Dependencies action: Add inputs (os, arch, compiler, compiler_version, cc, cxx)
- Dependencies action: Add 'Configure Conan' step after cache restore
- Dependencies action: Support both Linux and macOS profile generation
- Nix workflow: Remove 'Configure Conan' step, pass compiler params
- macOS workflow: Detect compiler version, pass to dependencies action

Benefits:
✅ Profile always fresh and correct for current matrix config
✅ Cache still includes .conan.db and other important files
✅ Self-contained dependencies action (easier to understand)
✅ Works for both Linux (with explicit cc/cxx) and macOS (auto-detect)

.github/actions/xahau-ga-dependencies/action.yml

@@ -25,6 +25,28 @@ inputs:
     description: 'Main branch name for restore keys'
     required: false
     default: 'dev'
+  os:
+    description: 'Operating system (Linux, Macos)'
+    required: false
+    default: 'Linux'
+  arch:
+    description: 'Architecture (x86_64, armv8)'
+    required: false
+    default: 'x86_64'
+  compiler:
+    description: 'Compiler type (gcc, clang, apple-clang)'
+    required: true
+  compiler_version:
+    description: 'Compiler version (11, 13, 14, etc.)'
+    required: true
+  cc:
+    description: 'C compiler executable (gcc-13, clang-14, etc.), empty for macOS'
+    required: false
+    default: ''
+  cxx:
+    description: 'C++ compiler executable (g++-14, clang++-14, etc.), empty for macOS'
+    required: false
+    default: ''
   stdlib:
     description: 'C++ standard library for Conan configuration (note: also in compiler-id)'
     required: true
@@ -63,6 +85,58 @@ runs:
         aws-access-key-id: ${{ inputs.aws-access-key-id }}
         aws-secret-access-key: ${{ inputs.aws-secret-access-key }}
 
+    - name: Configure Conan
+      shell: bash
+      run: |
+        # Create the default profile directory if it doesn't exist
+        mkdir -p ~/.conan2/profiles
+
+        # Determine the correct libcxx based on stdlib parameter
+        if [ "${{ inputs.stdlib }}" = "libcxx" ]; then
+          LIBCXX="libc++"
+        else
+          LIBCXX="libstdc++11"
+        fi
+
+        # Create profile with our specific settings
+        # This overwrites any cached profile to ensure fresh configuration
+        cat > ~/.conan2/profiles/default <<EOF
+        [settings]
+        arch=${{ inputs.arch }}
+        build_type=${{ inputs.configuration }}
+        compiler=${{ inputs.compiler }}
+        compiler.cppstd=20
+        compiler.libcxx=${LIBCXX}
+        compiler.version=${{ inputs.compiler_version }}
+        os=${{ inputs.os }}
+        EOF
+
+        # Add buildenv and conf sections for Linux (not needed for macOS)
+        if [ "${{ inputs.os }}" = "Linux" ] && [ -n "${{ inputs.cc }}" ]; then
+          cat >> ~/.conan2/profiles/default <<EOF
+
+        [buildenv]
+        CC=/usr/bin/${{ inputs.cc }}
+        CXX=/usr/bin/${{ inputs.cxx }}
+
+        [conf]
+        tools.build:compiler_executables={"c": "/usr/bin/${{ inputs.cc }}", "cpp": "/usr/bin/${{ inputs.cxx }}"}
+        EOF
+        fi
+
+        # Add macOS-specific conf if needed
+        if [ "${{ inputs.os }}" = "Macos" ]; then
+          cat >> ~/.conan2/profiles/default <<EOF
+
+        [conf]
+        # Workaround for gRPC with newer Apple Clang
+        tools.build:cxxflags=["-Wno-missing-template-arg-list-after-template-kw"]
+        EOF
+        fi
+
+        # Display profile for verification
+        conan profile show
+
     - name: Export custom recipes
       shell: bash
       run: |