Fix build warnings across workspace

- Remove redundant token fields from StreamEvent::Finished (data
  already delivered via Usage event)
- Remove dead hotkey_adjust_sampling, MAX_HISTORY, now()
- Fix unused variable warnings (delta, log)
- Suppress deserialization-only field warnings (jsonrpc, role)
- Make start_stream/chat_completion_stream_temp pub(crate)
- Remove unnecessary pub(crate) re-export of internal types

Remaining warnings are TODO items: SkipIndex (scoring not wired),
notify (MCP notifications not wired).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/subconscious/digest.rs

@@ -263,7 +263,7 @@ fn generate_digest(
         .join(".consciousness/logs/llm/digest");
     std::fs::create_dir_all(&log_dir).ok();
     let log_path = log_dir.join(format!("{}.txt", crate::store::compact_timestamp()));
-    let log = move |msg: &str| {
+    let _log = move |msg: &str| {
         use std::io::Write;
         if let Ok(mut f) = std::fs::OpenOptions::new()
             .create(true).append(true).open(&log_path)