feat(integrations): add MiniMax Code (mcode) agent integration (#4644)

[philo-x]

Description

Adds MiniMax Code (an AI coding assistant CLI, binary mcode) as a supported Spec Kit integration under the canonical key mcode.

MiniMax Code discovers project skills natively at .minimax/skills/<skill-name>/SKILL.md (runtime source workspace-minimax, priority 65) and invokes them via its slash shortcut (/speckit-<command>). This wires it up as a SkillsIntegration with its own isolated .minimax/skills layout (multi_install_safe=True).

Headless dispatch uses mcode exec "<prompt>", with optional --model and --output-format json support, verified against mcode exec --help.

Closes #4644

Test selection reasoning

Changed file	Affects	Test	Why
src/specify_cli/integrations/mcode/__init__.py (+ registry wiring)	new mcode integration, specify init scaffolding	T1	New integration install path; CLI scaffolding change requires at minimum /speckit.specify
src/specify_cli/_invocation_style.py	slash-invocation rendering in init next-steps and hook invocations	T1	Invocation display feeds every command's guidance
src/specify_cli/commands/init.py	specify init next-steps output	T1	Init scaffolding change
integrations/catalog.json	specify integration search/info discovery	T2, T3	Catalog discovery and metadata
docs/reference/integrations.md, issue templates, agent-context-defaults.json	docs / issue forms / agent-context extension	—	No slash-command behavior

Required tests

• T1: /speckit.specify (invoked as /speckit-specify) — new mcode integration install path + init scaffolding + live agent skill execution
• T2: specify integration search mcode — catalog discovery
• T3: specify integration info mcode — catalog metadata

Manual test results

Agent: MiniMax Code (mcode 0.4.12 via @minimax-ai/code@latest) | OS/Shell: macOS 15.6 / zsh

Command tested	Notes
Setup: specify init ... --integration mcode --non-interactive --script sh	PASS — mcode executable detected on PATH (no --ignore-agent-tools needed); scaffolded 10 skills under .minimax/skills/speckit-*/SKILL.md; next steps correctly rendered dash-notation slash commands /speckit-constitution, /speckit-specify, /speckit-plan, etc.
Runtime skill discovery: mcode exec "What skills are available in this project?"	PASS — MiniMax Code actively scanned .minimax/skills/ and listed all local Spec Kit workflow skills (speckit-specify, speckit-clarify, speckit-plan, speckit-tasks, etc.) as project-local skills.
T1: mcode exec --permission full "/speckit-specify Add health check endpoint with uptime and memory metrics"	PASS — Full agent workflow execution verified: MiniMax Code discovered /speckit-specify, ran the feature allocation script, generated specs/001-health-check-endpoint/spec.md, completed checklists/requirements.md, and persisted feature state to .specify/feature.json.
T2: specify integration search mcode	PASS — found MiniMax Code (mcode) v1.0.0 with tags cli, skills.
T3: specify integration info mcode	PASS — reported MiniMax Code (mcode) v1.0.0, author spec-kit-core, Built-in integration.

Log excerpt: MiniMax Code execution of /speckit-specify (T1)

Specification complete and validated. Here's the summary:

## Completion Report

**Feature**: Health Check Endpoint (feature #001)

- **SPECIFY_FEATURE_DIRECTORY**: specs/001-health-check-endpoint
- **SPEC_FILE**: specs/001-health-check-endpoint/spec.md
- **Checklist**: specs/001-health-check-endpoint/checklists/requirements.md
- Feature context persisted to .specify/feature.json for downstream commands

**What the spec covers**
- 3 prioritized user stories: P1 manual status view (status + uptime + memory), P2 automated monitoring integration (stable machine-readable responses), P3 early warning when memory usage is high
- 8 functional requirements (FR-001–FR-008), each testable
- 5 measurable, technology-agnostic success criteria
- Key entities: Health Status, Uptime, Memory Usage
- Assumptions documenting defaults and out-of-scope items

**Validation results**: All 16 quality checklist items passed on iteration 1. No [NEEDS CLARIFICATION] markers remain.

Automated test results

Ran with .venv/bin/python -m pytest per CONTRIBUTING guidance.

Integration & consistency suites

.venv/bin/python -m pytest \
  tests/integrations/test_integration_mcode.py \
  tests/integrations/test_registry.py \
  tests/test_agent_config_consistency.py -q

Result: 896 passed in 48.11s.

Full test suite

.venv/bin/python -m pytest tests -q

Result: 8,079 passed, 207 skipped, 1 failed.

The single failure, test_ps_variant_prefixed_with_powershell_launcher, is unrelated to this PR and is caused by the absence of pwsh/powershell on macOS.

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (fill in the disclosure below)

AI disclosure: Prepared with AI assistance. ChatGPT (GPT-5.6 Sol) was used to review the integration design, validate the Spec Kit and MiniMax Code architecture, and identify the relevant integration surfaces. Antigravity (Gemini 3.8 Flash, High, autonomous) was used on behalf of @philo-x for implementation, test authoring, end-to-end mcode workflow verification, and documentation alignment.