refactor(cr-2026-04-22): remove dead code and stale allow(dead_code) suppressions

2026-04-22 review MINORs and NITs:

- crates/core/src/providers.rs: delete entire module. SpeechToText /
  TextProcessor / ProviderRegistry were forward-looking traits that
  never got wired — the Transcriber trait in kon-transcription
  (A.2 #13) has since superseded SpeechToText, and the Registry
  pattern was redundant against LocalEngine. Keeping them as dead
  public surface signalled future direction that is no longer
  accurate.
- crates/core/src/types.rs: delete TranscriptMetadata. Forward-
  looking struct with an unfulfilled TODO; storage has evolved
  independently through v7/v8 migrations without adopting it.
- crates/ai-formatting/src/llm_client.rs: remove #[allow(dead_code)]
  from CLEANUP_PROMPT and format_dictionary_suffix. Both are
  actively called; the suppressions would hide future genuine
  dead-code warnings in this regression-sensitive prompt file.
- src-tauri/src/commands/live.rs: remove #[allow(dead_code)] from
  LiveStatusMessage. Every variant (Warning, Overload, Error,
  Finished) is constructed in the module today.
- README.md: update kon-transcription row from "SpeechToText
  trait" to "Transcriber trait" and mention the new streaming/
  module.

Workspace test gate green (225 lib tests across all crates).

crates/core/src/lib.rs

@@ -3,12 +3,11 @@ pub mod error;
 pub mod hardware;
 pub mod model_registry;
 pub mod process_watch;
-pub mod providers;
 pub mod recommendation;
 pub mod types;
 
 pub use error::{KonError, Result};
 pub use types::{
     AudioSamples, DownloadProgress, EngineName, Megabytes, ModelId, Segment, Transcript,
-    TranscriptMetadata, TranscriptionOptions,
+    TranscriptionOptions,
 };

crates/core/src/providers.rs

@@ -1,40 +0,0 @@
-use std::sync::Arc;
-
-use async_trait::async_trait;
-
-use crate::error::Result;
-use crate::types::{AudioSamples, EngineName, Transcript, TranscriptionOptions};
-
-/// Any speech-to-text engine implements this trait.
-/// Base types know nothing about their derivatives.
-#[async_trait]
-pub trait SpeechToText: Send + Sync {
-    async fn transcribe(
-        &self,
-        audio: AudioSamples,
-        options: &TranscriptionOptions,
-    ) -> Result<Transcript>;
-
-    fn name(&self) -> &EngineName;
-
-    fn is_available(&self) -> bool;
-}
-
-/// Any text post-processor implements this trait.
-#[async_trait]
-pub trait TextProcessor: Send + Sync {
-    async fn process(&self, text: &str, instruction: &str) -> Result<String>;
-
-    fn name(&self) -> &EngineName;
-
-    fn is_available(&self) -> bool;
-}
-
-/// Holds the active provider instances. Constructed at startup,
-/// rebuilt when user changes provider in settings.
-// TODO: Wire into Tauri app state once multi-engine switching is implemented.
-#[allow(dead_code)]
-pub struct ProviderRegistry {
-    pub stt: Arc<dyn SpeechToText>,
-    pub text: Option<Arc<dyn TextProcessor>>,
-}

crates/core/src/types.rs

@@ -166,23 +166,6 @@ pub struct TranscriptionOptions {
     pub initial_prompt: Option<String>,
 }
 
-/// Full provenance metadata for a transcript.
-/// Captures everything needed to reproduce the transcription.
-// TODO: Attach to Transcript once the store layer persists transcription provenance.
-#[allow(dead_code)]
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct TranscriptMetadata {
-    pub engine: String,
-    pub model_id: ModelId,
-    pub inference_ms: u64,
-    pub sample_rate: u32,
-    pub audio_channels: u16,
-    pub format_mode: String,
-    pub remove_fillers: bool,
-    pub british_english: bool,
-    pub anti_hallucination: bool,
-}
-
 /// Progress update during model download.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct DownloadProgress {