Delete ui_channel.rs — relocate types, remove all UiMessage/UiSender plumbing

Types relocated:
- StreamTarget → mind/mod.rs (Mind decides Conversation vs Autonomous)
- SharedActiveTools + shared_active_tools() → agent/tools/mod.rs
- ContextSection + SharedContextState → agent/context.rs (already there)
- StatusInfo + ContextInfo → user/mod.rs (UI display state)

Removed UiSender from: Agent::turn, Mind, learn.rs, all function signatures.
The entire message-passing layer is gone. All state flows through
Agent fields (activities, entries, streaming) read by the UI via try_lock.

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

src/subconscious/learn.rs

@@ -17,7 +17,6 @@
 use crate::agent::api::ApiClient;
 use crate::agent::api::types::*;
 use crate::agent::context::{ConversationEntry, ContextState};
-use crate::user::ui_channel::UiSender;
 
 const SCORE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(120);
 
@@ -181,7 +180,6 @@ impl MemoryScore {
 pub async fn score_memories(
     context: &ContextState,
     client: &ApiClient,
-    ui_tx: &UiSender,
 ) -> anyhow::Result<MemoryScore> {
     let mut memory_keys: Vec<String> = context.entries.iter()
         .filter_map(|e| match e {
@@ -272,7 +270,6 @@ pub async fn score_memory(
     context: &ContextState,
     key: &str,
     client: &ApiClient,
-    ui_tx: &UiSender,
 ) -> anyhow::Result<f64> {
     const RESPONSE_WINDOW: usize = 50;
 
@@ -309,7 +306,6 @@ pub async fn score_memories_incremental(
     max_age_secs: i64,
     response_window: usize,
     client: &ApiClient,
-    ui_tx: &UiSender,
     agent: &std::sync::Arc<tokio::sync::Mutex<crate::agent::Agent>>,
 ) -> anyhow::Result<Vec<(String, f64)>> {
     let now = chrono::Utc::now().timestamp();
@@ -387,7 +383,6 @@ pub async fn score_finetune(
     context: &ContextState,
     count: usize,
     client: &ApiClient,
-    ui_tx: &UiSender,
 ) -> anyhow::Result<Vec<(usize, f64)>> {
     let range = context.entries.len().saturating_sub(count)..context.entries.len();