chore(install): add reproducible local setup

docs/installation-log-2026-08-11.md

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+# Installation Record — 2026-08-11
+
+This record captures the successful local source installation performed on an Apple Silicon macOS host. It contains no credentials or machine-specific home-directory path.
+
+## Environment
+
+```text
+Architecture: arm64
+Python: 3.11.15
+Installer: uv 0.11.8
+Virtual environment: <repository>/.venv
+Launcher: ~/.local/bin/cowork-local
+Installed size: approximately 1.3 GB
+```
+
+## Steps executed
+
+From the repository root:
+
+```bash
+git switch -c chore/local-installation
+./scripts/install_local.sh
+```
+
+The installer selected Homebrew Python 3.11, created `.venv`, installed the runtime and test requirement sets, and created the user launcher without replacing any existing path.
+
+Key resolved packages:
+
+```text
+PySide6==6.11.1
+anyio==4.14.2
+holidays==0.102
+keyring==25.7.0
+mcp==1.29.0
+msal==1.37.0
+networkx==3.6.1
+openpyxl==3.1.5
+psutil==7.2.2
+pydantic==2.13.4
+Pygments==2.20.0
+python-pptx==1.0.2
+requests==2.34.2
+pytest==9.1.1
+```
+
+## Verification executed
+
+```bash
+.venv/bin/python -m pytest tests -q
+.venv/bin/python -c "import PySide6, pydantic, requests"
+```
+
+Additional verification imported every module under `cowork_local` with `QT_QPA_PLATFORM=offscreen`, then started the real application entry point with a 1.5-second automatic Qt shutdown.
+
+Results:
+
+```text
+Tests: 81 passed
+Runtime dependency imports: PASS
+Application module imports: 0 failures
+Headless startup: exit 0
+Launcher in PATH: PASS
+```
+
+Qt emitted one non-fatal warning while populating the fallback alias for the missing `Sans Serif` family. It did not affect application startup.
+
+## Optional capabilities
+
+`pypdf` and `opendataloader-pdf` were intentionally not installed in the baseline environment. Install `requirements-optional.txt` when advanced PDF extraction is required. A `soffice` command was detected on the installation host, but LibreOffice availability remains an external host prerequisite rather than a Python dependency.
+
+No provider credential, unlock code, token, or application state was written to the repository during installation or verification.