docs: add Access support design and implementation plan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/plans/2026-05-11-access-support-design.md

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+# Access (.accdb) VBA Code Export/Import Support Design
+
+## Summary
+
+Extend the existing `extract_vba.py` and `import_vba.py` to support Access `.accdb` files alongside Excel `.xlsm` files. The file type is auto-detected by extension via a unified `TARGET_FILE` env variable.
+
+## Key COM Differences
+
+| Dimension | Excel (.xlsm) | Access (.accdb) |
+|-----------|---------------|-----------------|
+| ProgID | `Excel.Application` | `Access.Application` |
+| Open | `Workbooks.Open(path)` | `OpenCurrentDatabase(path)` |
+| VBA Project | `workbook.VBProject` | `CurrentDb().VBE.VBProjects(1)` |
+| Close | `workbook.Close()` + `Quit()` | `CloseCurrentDatabase()` + `Quit()` |
+| Module types | Standard/Class/Document/Forms | Standard/Class only |
+
+## Changes
+
+### .env
+- Replace `TARGET_XLSM_FILE` with `TARGET_FILE` (supports `.xlsm` and `.accdb`)
+
+### extract_vba.py
+- Replace `TARGET_XLSM_FILE` with `TARGET_FILE`
+- Add `extract_vba_modules_access_com()` method to `VBAExtractor`
+- Update `main()` to detect file type by extension and auto-select COM method
+- Skip olevba option for `.accdb` files (unsupported)
+
+### import_vba.py
+- Replace `TARGET_XLSM_FILE` with `TARGET_FILE`
+- Add `import_vba_access()` method to `VBAImporter`
+- Update `main()` to detect file type by extension and route accordingly
+
+## Out of Scope
+- Access Forms/Reports VBA code (user doesn't need it)
+- olevba for Access files (unsupported)
+- Directory structure changes (Modules/ClassModules sufficient)