Add Windows support

Windows joins the three systems as its own entry in each table: DirectShow
through ffmpeg for capture, the Win32 clipboard and SendInput for the paste,
RegisterHotKey for the global shortcut, and the whisper.cpp and llama.cpp
Windows zips (the OpenBLAS whisper build, which transcribes about twice as
fast on a plain CPU). Settings go to APPDATA, data to LOCALAPPDATA, and
install.ps1 adds the Start Menu entry, the dikte command and an optional
autostart. Meetings are not supported yet: Windows offers nothing to record
the far side from.

Porting surfaced three fixes that were not Windows specific:

- A stopped or overlong download tried to delete its .part file while still
  holding it open, which Windows refuses. The unlinks now wait for the handle.
- The CLI transcribed files without handing the local servers their settings
  first, so a local provider failed with "no model downloaded" wherever the
  GUI had not run in the same process.
- The audio content types are pinned instead of asked of the registry, which
  answers differently machine to machine.

One fix is Windows specific but sits in shared code: shutdown() does not end
a blocked recv there, so stopping a request also closes the socket handle.

Co-Authored-By: Claude Fable 5 <[email protected]>

README.windows.md

@@ -0,0 +1,72 @@
+# Dikte on Windows
+
+Press `Ctrl+Space`, talk, press again: what you said is transcribed, cleaned
+up and pasted where your cursor is.
+
+## Requirements
+
+- **Windows 10/11**
+- **Python 3.11+** with **PyQt6** (`pip install PyQt6`; install.ps1 installs
+  it when it is missing)
+- **ffmpeg** for microphone capture: `winget install Gyan.FFmpeg`
+
+## Installing
+
+```powershell
+powershell -ExecutionPolicy Bypass -File install.ps1
+```
+
+This adds a **Dikte** entry to the Start Menu and a **`dikte`** command to the
+terminal. Add `-Autostart` to also start it at sign-in; `-Uninstall` removes
+all of it and leaves the repository and your settings alone.
+
+To try it without installing anything:
+
+```sh
+python dikte.py
+```
+
+## First run
+
+1. The tray icon appears and the Settings window opens.
+2. Under **API and models**, download a local whisper model (the whisper.cpp
+   Windows build is fetched automatically) or enter an OpenAI, Groq or
+   OpenRouter key.
+3. The shortcut defaults to `Ctrl+Space` and is changed under Shortcuts.
+   While Dikte runs, Windows' own hotkey service (RegisterHotKey) listens for
+   it: nothing to install and no permission to grant.
+
+## What is different from Linux and macOS
+
+- **Meeting recording (microphone + speakers) is not supported yet.** Windows
+  does not offer what the speakers are playing as a capture device, so there
+  is nothing to record the far side from. Everything else works, including
+  transcribing audio and video files.
+- **The shortcut is swallowed**: while Dikte holds `Ctrl+Space`, the focused
+  application does not see it. This is how macOS behaves too, and unlike the
+  Linux listener, which shares the key.
+- No external tools for the clipboard or the key press: both go straight
+  through the Windows API (the clipboard, SendInput).
+- Settings live under `%APPDATA%\Dikte`, models and recordings under
+  `%LOCALAPPDATA%\Dikte`.
+
+## Performance
+
+- The local install fetches whisper.cpp's **OpenBLAS build**, which
+  transcribes about twice as fast as the stock one on a plain CPU. There is
+  no GPU build to fetch for machines without an NVIDIA card.
+- Setting Settings → API and models → **Threads** near your physical core
+  count helps noticeably; the server's own default is 4.
+- If speed matters more than accuracy, `ggml-small` and `ggml-base` are much
+  faster; `ggml-large-v3-turbo-q5_0` transcribes best.
+
+## Troubleshooting
+
+- **Recording does not start:** does `ffmpeg -version` run? Does
+  `dikte devices` list your microphone?
+- **Nothing is pasted:** a normal-privilege process cannot type into an
+  elevated (administrator) window; run Dikte elevated too, or paste by hand.
+  The text lands on the clipboard either way.
+- **The shortcut does nothing:** another application already holds the
+  combination. Dikte says so in a tray notification when it asks for the key;
+  pick a different one under Settings → Shortcuts.