Put the three providers in a table, and test the request rather than the list

Reworked on top of master. The Groq request itself needed nothing beyond a key,
a base URL and a model id, but two providers fit in an if and an else where
three do not, and each one was written out four times: in transcribe_target(),
in the key rows of the settings window, in save and in load.

config.TRANSCRIBERS holds them now, one row each: the name the user sees and
the three settings that keep its key, its endpoint and its model. The variable
an empty key falls back to is the name of its setting, shouted. The provider
box, save, load, `dikte models --provider` and `dikte test-key` all read that
table, so a fourth provider is a row and a default rather than a branch in five
files. The key field, its Test button and its answer line are built once and
the three signals became one that carries which key was asked about.

The tests moved into the files of the modules they cover and check what a
provider actually changes: that the request goes to api.groq.com with the right
model and fields, that the glossary now reaches everything except OpenRouter,
that a Groq error says Groq, and that the settings window carries the key and
the model there and back. GROQ_API_KEY is cleared for the test run like the
other two, so a developer who has one does not send a test to the network.

Co-authored-by: Muzaffer Emre <[email protected]>

README.md

@@ -39,10 +39,10 @@ sudo apt install pulseaudio-utils xclip xdotool ffmpeg
 `install.sh` adds the `dikte` command, a menu entry and an autostart entry. The
 settings window installs a GNOME or KDE global shortcut.
 
-The settings window accepts **OpenAI**, **Groq** and **OpenRouter** keys. Speech
-to text runs on any of them (`gpt-4o-transcribe` by default), cleanup always on
-OpenRouter (`google/gemini-3.5-flash-lite`), so a single OpenRouter key can
-cover both. They fall back to `OPENAI_API_KEY`, `GROQ_API_KEY` and
+Three keys go in the settings window: **OpenAI**, **Groq** and **OpenRouter**.
+Speech to text runs on any of them (`gpt-4o-transcribe` by default), cleanup
+always on OpenRouter (`google/gemini-3.5-flash-lite`), so a single OpenRouter key
+can cover both. They fall back to `OPENAI_API_KEY`, `GROQ_API_KEY` and
 `OPENROUTER_API_KEY`, and are
 stored in `~/.config/dikte/config.json`, mode 600. Cleanup can be switched off,
 in which case the raw transcript is pasted, and a thinking model's effort can be