chore: bump minimum Python from 3.8 to 3.9 (#336)

* chore: bump minimum Python from 3.8 to 3.9 and adopt PEP 585 builtins

- Update requires-python, classifiers, mypy target, and black target in pyproject.toml
- Replace Python 3.8 with 3.9 in CI matrix and nightly workflow
- Replace typing.List/Dict/Tuple/Set with builtin list/dict/tuple/set (PEP 585)
- Update all 3.8 version references in README, docs, website, and install.sh
- Fix test_wayland_no_tools to mock IBus availability
- Remove List from common_types re-exports and update test

* style: reformat test files for Black 26.x and pin version in CI

Black 26.x introduced parenthesized context manager formatting.
Reformat 7 test files and pin Black>=26,<27 in CI to prevent
future drift from unpinned version upgrades.

docs/DISTRO_COMPATIBILITY.md

@@ -112,7 +112,7 @@ sudo zypper install -y python3-gobject python3-gobject-cairo gtk3 \
 ### Gentoo
 ```bash
 sudo emerge dev-python/pygobject:3 x11-libs/gtk+:3 dev-libs/libappindicator:3 \
-  media-libs/portaudio dev-lang/python:3.8
+  media-libs/portaudio dev-lang/python:3.9
 ```
 
 **Note:** Gentoo compiles packages from source, which will take longer.

docs/INSTALL.md

@@ -31,7 +31,7 @@ git clone https://github.com/jatinkrmalik/vocalinux.git && cd vocalinux && ./ins
 | Requirement | Details |
 |-------------|---------|
 | **Operating System** | Ubuntu 22.04+ (recommended), Debian 11+, Fedora 38+, Arch Linux |
-| **Python** | 3.8 or newer |
+| **Python** | 3.9 or newer |
 | **Display Server** | X11 or Wayland |
 | **Hardware** | Microphone for speech input |
 | **Disk Space** | ~200MB (including whisper.cpp model) |