Add SpeechToDeck to Plugin Store

[rusagent]

Add SpeechToDeck to Plugin Store

Adds a microphone button to the Steam virtual keyboard. Press it, speak, press
it again: the full utterance is transcribed locally by a pinned Voxtype
(whisper.cpp) runtime and the complete transcript is inserted into the text
field as one bulk paste action — no cloud services, no accounts, no
per-character typing, no auto-submit. Multilingual by default (whisper base),
VAD to reject silence-only input, clipboard-only mode as an explicit fallback.

This PR adds the plugin as a submodule pinned to the release commit.

Task Checklist

Developer

• I am the original author or an authorized maintainer of this plugin.
• I have abided by the licenses of the libraries I am utilizing, including
  attaching license notices where appropriate.
  (THIRD_PARTY_NOTICES.md: whisper.cpp MIT, Voxtype MIT, React MIT, Decky
  MIT.)
• OWNER: Generative AI was NOT used to write a majority of the code I
  am submitting.
  

Plugin

• OWNER: I have verified that my plugin works properly on the Stable
  and Beta update channels of SteamOS.
  
• I have verified my plugin is unique or provides more/alternative
  functionality to a plugin already on the store.
  (No existing store plugin adds a dictation button to the Steam virtual
  keyboard with local bulk-insert transcription.)

Backend

• No: I am using a custom backend other than Python.
• Yes: I am using a tool or software from a 3rd party FOSS project that
  does not have it's dependencies statically linked.
  (Voxtype v1.0.1, MIT, https://github.com/peteonrails/voxtype — dynamically
  linked against glibc; delivered via package.json remote_binary with pinned
  sha256.)
• No: I am using a custom binary that has all of it's dependencies
  statically linked.

Community

• I have tested and left feedback on two other pull requests for
  new or updating plugins.
  
• I have commented links to my testing report in this PR.
  

Testing

• Tested by a third party on SteamOS Preview update channel.
  

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