tools: delete dispatch_shared, use dispatch everywhere

dispatch_shared was a legacy wrapper — replaced by dispatch() which
goes through the unified Tool registry. One dispatch path for all
callers (interactive agent, subconscious agents, MCP server).

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

src/agent/tools/mod.rs

@@ -144,23 +144,6 @@ pub async fn dispatch_with_agent(
     }
 }
 
-/// Dispatch shared tools — used by subconscious agents.
-pub async fn dispatch_shared(
-    name: &str,
-    args: &serde_json::Value,
-    _provenance: Option<&str>,
-) -> Option<String> {
-    for tool in tools() {
-        if tool.name == name {
-            return Some(match (tool.handler)(None, args.clone()).await {
-                Ok(s) => s,
-                Err(e) => format!("Error: {}", e),
-            });
-        }
-    }
-    None
-}
-
 /// Return all registered tools with definitions + handlers.
 pub fn tools() -> Vec<Tool> {
     let mut all = vec![