llm: drop model/agent scope matching; add instance-wide compaction model picker

Remove the scope system end-to-end (llm_models.scope column, agent meta
scope field, scope-based tier in model selection, UI checkboxes/pills):
it was only a soft ranking hint, had drifted (6 UI scopes vs 3 used by
agents, 'general' not even selectable) and duplicated what strength
already decides. Strength stays the single AUTO-selection axis.

Compaction: the summary model is now pickable from the Settings page
via a new PropertyType::LlmModel config property (registry key
compaction_model), instance-wide and live (no restart). Fallback chain:
explicit pick -> compaction.strength from config.yml -> priority order;
a deleted configured model degrades to AUTO. ContextCompactor reads the
key at compact time through GlobalConfigManager.

crates/skald-core/src/session/handler/agent_dispatch.rs

@@ -57,7 +57,6 @@ impl ChatSessionHandler {
         let explicit_client = args["client"].as_str().or(target_meta.client.as_deref());
         let (resolved_client, _) = self.llm_manager.resolve(
             explicit_client,
-            target_meta.scope.as_deref(),
             target_meta.strength,
         ).await.map_err(|e| anyhow::anyhow!("dispatch_sub_agent: {e}"))?;
 
@@ -241,7 +240,7 @@ impl ChatSessionHandler {
         let meta = crate::agents::load_task_meta(&frame.agent_id)
             .map_err(|e| anyhow::anyhow!("resume: cannot load sub-agent `{}`: {e}", frame.agent_id))?;
         let (client, _) = self.llm_manager.resolve(
-            meta.client.as_deref(), meta.scope.as_deref(), meta.strength,
+            meta.client.as_deref(), meta.strength,
         ).await?;
         self.build_sub_agent_config(root_config, &frame.agent_id, client.to_string(), frame.id, frame.depth).await
     }

crates/skald-core/src/session/handler/config.rs

@@ -50,7 +50,6 @@ impl ChatSessionHandler {
         let meta = crate::agents::load_meta(&self.agent_id).ok();
         let (key, _) = self.llm_manager.resolve(
             client_name.as_deref(),
-            meta.as_ref().and_then(|m| m.scope.as_deref()),
             meta.as_ref().and_then(|m| m.strength),
         ).await?;
 

crates/skald-core/src/session/handler/llm_call.rs

@@ -45,7 +45,6 @@ impl ChatSessionHandler {
         stack_id:      i64,
         config:        &AgentRunConfig,
         active_grants: &HashSet<String>,
-        req_scope:     Option<&str>,
         req_strength:  Option<LlmStrength>,
         cur_name:      &mut String,
         cur_llm:       &mut Arc<LlmEntry>,
@@ -155,7 +154,7 @@ impl ChatSessionHandler {
             }
 
             let excluded: Vec<&str> = tried_this_round.iter().map(String::as_str).collect();
-            match self.llm_manager.select_excluding(&excluded, req_scope, req_strength).await {
+            match self.llm_manager.select_excluding(&excluded, req_strength).await {
                 Ok((next_name, next_llm)) => {
                     warn!(session_id = self.session_id, from = %cur_name, to = %next_name, "LLM fallback");
                     em.model_fallback(cur_name.clone(), next_name.clone(), first_line(&e.to_string())).await;

crates/skald-core/src/session/handler/llm_loop.rs

@@ -65,9 +65,8 @@ impl ChatSessionHandler {
         let mut cur_llm  = self.llm_manager.get(&cur_name).await
             .ok_or_else(|| anyhow::anyhow!("LLM client '{}' not found", cur_name))?;
 
-        // Scope/strength needed for fallback re-selection.
+        // Strength needed for fallback re-selection.
         let meta         = crate::agents::load_meta(&config.agent_id).ok();
-        let req_scope    = meta.as_ref().and_then(|m| m.scope.as_deref()).map(str::to_string);
         let req_strength = meta.as_ref().and_then(|m| m.strength);
 
         // Accumulates tool calls across all rounds for the event bus.
@@ -132,7 +131,7 @@ impl ChatSessionHandler {
             // retriable errors. `cur_name`/`cur_llm`/`messages` are updated in place.
             let turn_result = match self.call_llm_round(
                 stack_id, config, &active_grants_snapshot,
-                req_scope.as_deref(), req_strength,
+                req_strength,
                 &mut cur_name, &mut cur_llm, &mut messages, token, &em,
             ).await {
                 RoundLlm::Turn(t)   => t,