feat(coding-agent): added plan mode with approval workflow and tool gating

- Plan mode provides structured workflow where agents propose plans for user approval before execution.
- Added plan:// internal URL protocol for accessing plan files and injecting plan-mode context into subagent prompts.
- Added plan mode toggle shortcut and paused status indicator in status line.
- Fixed plan reference injection to properly pass workflow state to plan-mode system prompts.
- Improved autocomplete fuzzy matching to support subsequence matching for skill suggestions.

packages/coding-agent/test/tools/python-fallback.test.ts

@@ -43,7 +43,7 @@ describe("createTools python fallback", () => {
 		const tools = await createTools(session, ["python"]);
 		const names = tools.map(tool => tool.name).sort();
 
-		expect(names).toEqual(["bash"]);
+		expect(names).toEqual(["bash", "exit_plan_mode"]);
 
 		availabilitySpy.mockRestore();
 	});