Slash‑commands ignored / arguments dropped when using Cursor CLI (cursor‑agent) — /speckit.* commands only send the command name

[arsalan98m]

Body:

## Description
When using Spec Kit with Cursor CLI as the agent, invoking any slash‑command (e.g. /speckit.constitution, /speckit.plan, /speckit.specify, etc.) results in only the command name being sent. The arguments or trailing text are dropped. As a result, Spec Kit does not generate the expected output (constitution file, spec, plan, tasks, etc.). This occurs consistently with Cursor CLI; other agents (e.g. Gemini‑CLI, Claude CLI) work correctly in the same setup.

## Environment

• OS: macOS 14.1
• Shell / terminal: zsh
• Spec Kit version: 0.0.22
• Cursor CLI / cursor‑agent version: 2025.11.25-d5b3271
• Project type: Next.js

## Steps to reproduce

1. Install Spec Kit and Cursor CLI / cursor‑agent in a new or existing project.

2. Run specify init --here or specify init . (or chosen initialization command), selecting cursor-agent.

3. In the agent prompt or terminal, enter a slash‑command with arguments, e.g.:

   /speckit.constitution Add project constitution for expense‑tracker
   

4. Observe that only /speckit.constitution appears (arguments are dropped).

5. No constitution file (or other output) is created; other slash‑commands behave the same way.

## Expected behavior
The command + arguments should be processed by Spec Kit. For example, /speckit.constitution <text> should cause Spec Kit to write the given text into .specify/memory/constitution.md. Similarly, /speckit.plan, /speckit.specify, /speckit.tasks should generate plan/spec/tasks accordingly.

## Actual behavior
Only the slash command name is recognized/sent; arguments are lost. Spec Kit does not produce the expected output (no files generated/updated).

## Additional observations

• Using other agents (e.g. Gemini‑CLI or Claude CLI) in the same environment works fine: slash‑commands + arguments are accepted and output is generated.
• specify check (or equivalent Spec Kit check commands) may or may not report cursor-agent as “found”, but the behavior persists regardless.
• No explicit error messages are shown. The behavior is “silent”: commands just don’t work as intended.

## Importance / Impact
This bug prevents using Spec Kit slash‑commands when Cursor CLI is chosen as the agent. For users who prefer or rely on Cursor CLI, this makes Spec Kit effectively unusable — undermining the spec‑driven workflow.

## Suggested next steps / questions

• Confirm whether cursor-agent integration is still officially supported, and on which versions.
• Investigate why arguments to slash‑commands are lost: is it due to argument parsing, agent‑detection, or terminal mode issues?
• Consider adding a diagnostic mode or explicit error message when slash‑commands fail under Cursor, to help users debug.