feat(FN-2703): support custom MCP tools in plan generation

- Remove ToolSearch prerequisite so custom MCP tools can be used during triage and plan generation flows
- Align built-in tool sets between provider wiring and prompt builder handling, including custom ls behavior
- Expand pi-claude-cli tests for event bridge, MCP config, prompt builder, and tool mapping regressions
- Add FN-2703 changeset and delivery documentation for the published @runfusion/fusion package

packages/pi-claude-cli/src/__tests__/tool-mapping.test.ts

@@ -228,6 +228,7 @@ describe("tool-mapping", () => {
     it("returns true for custom tool names", () => {
       expect(isCustomToolName("myTool")).toBe(true);
       expect(isCustomToolName("deploy")).toBe(true);
+      expect(isCustomToolName("ls")).toBe(true);
     });
 
     it("returns false for all 6 built-in tool names", () => {