refactor(mcp): centralize meta-function prefix predicates and fix list_tools pagination

Implements T1 of plans/mcp-resources-prompts-design.md (§4.1, §4.6):

- Replace list_tools(None) with cursor-following list_all_tools() at the
  three call sites (start_server catalog build, catalog_items, describe)
  so paginating servers no longer silently lose tools past page one.
- Add MCP_READ/MCP_PROMPT prefix constants (declared nowhere yet; wired
  in T4/T7) plus centralized helpers MCP_META_FUNCTION_PREFIXES,
  is_mcp_meta_function, and mcp_meta_function_names.
- Mechanically replace every hand-rolled 3-prefix starts_with triple
  (partition in eval_tool_calls, 3 exclusion triples in
  select_enabled_functions, 3 inclusion triples + per-server name
  construction in select_enabled_mcp_servers) with the helpers,
  preserving the existing lax starts_with matching semantics and the
  mcp_invoke_* enablement sentinel (sentinel moves to search in T5).
- Behavior-neutral: dispatch chains keep their 3 arms, emission stays
  at exactly 3 meta-functions per server, existing tests unmodified.
- Add unit tests: helper classification, prefix-soundness property,
  lax-matching pin, ordered candidate-name construction.

src/config/tool_scope.rs

@@ -63,10 +63,10 @@ impl McpRuntime {
             .get(server)
             .cloned()
             .with_context(|| format!("{server} MCP server not found in runtime"))?;
-        let tools = server_handle.list_tools(None).await?;
+        let tools = server_handle.list_all_tools().await?;
         let mut items = HashMap::new();
 
-        for tool in tools.tools {
+        for tool in tools {
             let item = CatalogItem {
                 name: tool.name.to_string(),
                 server: server.to_string(),
@@ -110,9 +110,8 @@ impl McpRuntime {
             .with_context(|| format!("{server} MCP server not found in runtime"))?;
 
         let tool_schema = server_handle
-            .list_tools(None)
+            .list_all_tools()
             .await?
-            .tools
             .into_iter()
             .find(|item| item.name == tool)
             .ok_or_else(|| anyhow!("{tool} not found in {server} MCP server catalog"))?