feat: add path_to_bun_executable input for custom Bun installations (#481)

* feat: add path_to_bun_executable input for custom Bun installations

Adds optional input to specify a custom Bun executable path, bypassing automatic installation. This enables:
- Using pre-installed Bun binaries for faster workflow runs
- Testing with specific Bun versions for debugging
- Custom installation paths in unique environments

Follows the same pattern as path_to_claude_code_executable input.

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

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

* refactor: consolidate custom executable tests into single workflow

- Remove separate test-custom-executable.yml workflow
- Rename test-custom-bun.yml to test-custom-executables.yml
- Add comprehensive tests for custom Claude, custom Bun, and both together
- Improve verification steps with better error handling

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

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

* simplify: test workflow to single job testing both custom executables

- Remove individual test jobs for Claude and Bun
- Keep only the combined test that validates both custom executables work together
- Simplifies CI workflow and reduces redundant testing

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

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

base-action/action.yml

@@ -91,6 +91,10 @@ inputs:
     description: "Optional path to a custom Claude Code executable. If provided, skips automatic installation and uses this executable instead. WARNING: Using an older version may cause problems if the action begins taking advantage of new Claude Code features. This input is typically not needed unless you're debugging something specific or have unique needs in your environment."
     required: false
     default: ""
+  path_to_bun_executable:
+    description: "Optional path to a custom Bun executable. If provided, skips automatic Bun installation and uses this executable instead. WARNING: Using an incompatible version may cause problems if the action requires specific Bun features. This input is typically not needed unless you're debugging something specific or have unique needs in your environment."
+    required: false
+    default: ""
 
 outputs:
   conclusion:
@@ -110,10 +114,20 @@ runs:
         cache: ${{ inputs.use_node_cache == 'true' && 'npm' || '' }}
 
     - name: Install Bun
+      if: inputs.path_to_bun_executable == ''
       uses: oven-sh/setup-bun@735343b667d3e6f658f44d0eca948eb6282f2b76 # https://github.com/oven-sh/setup-bun/releases/tag/v2.0.2
       with:
         bun-version: 1.2.11
 
+    - name: Setup Custom Bun Path
+      if: inputs.path_to_bun_executable != ''
+      shell: bash
+      run: |
+        echo "Using custom Bun executable: ${{ inputs.path_to_bun_executable }}"
+        # Add the directory containing the custom executable to PATH
+        BUN_DIR=$(dirname "${{ inputs.path_to_bun_executable }}")
+        echo "$BUN_DIR" >> "$GITHUB_PATH"
+
     - name: Install Dependencies
       shell: bash
       run: |
@@ -161,6 +175,7 @@ runs:
         INPUT_FALLBACK_MODEL: ${{ inputs.fallback_model }}
         INPUT_EXPERIMENTAL_SLASH_COMMANDS_DIR: ${{ inputs.experimental_slash_commands_dir }}
         INPUT_PATH_TO_CLAUDE_CODE_EXECUTABLE: ${{ inputs.path_to_claude_code_executable }}
+        INPUT_PATH_TO_BUN_EXECUTABLE: ${{ inputs.path_to_bun_executable }}
 
         # Provider configuration
         ANTHROPIC_API_KEY: ${{ inputs.anthropic_api_key }}