[echarrod]

Description

Refs #2654. Follow-up to #4919 (Claude) and #5116 (Droid).

Adds a Mistral Vibe-only integration option:

specify init my-project --integration vibe --integration-options="--no-model-invocation"

• It writes disable-model-invocation: true on the core speckit-* command skills, including preset overrides of them. Mistral Vibe's README says such a skill is explicit-only: users can still invoke /skill-name, but the model does not see or invoke it automatically. The default is unchanged.
• Extension skills stay model-invocable, because mandatory hooks such as git's speckit.git.feature need the model to invoke them.
• The option persists through integration.json, so specify integration upgrade vibe reapplies it.

Differences from Droid:

• Vibe's README says the model does not see the skill, so unlike Droid the context-budget benefit is documented upstream. I did not measure it.
• Vibe already had options (--skills, --events); this adds a third.
• The frontmatter stem helper already existed, so it now reuses a shared name parser rather than duplicating one.
• Like Droid, Vibe is multi_install_safe, so the lifecycle caveats (preset add/remove/update, bundles, integration use, switch when not default, upgrade --force) carry over unchanged.

Only the Vibe package, its tests and docs/integrations/vibe.md change; no shared base.py change.

AI Disclosure

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

AI disclosure: Written for @echarrod by Claude Code (claude-sonnet-5-5) running autonomously. It wrote the code, tests and docs, ran the test suite and an automated /code-review medium. @echarrod reviewed it before marking it ready.