When no LLM provider is configured, hovering the disabled "Generate
Commit Message" button in the git panel/commit modal previously showed a
plain, non-interactive tooltip with no way to act on it.

This tooltip now includes two links:
- **Configure Provider** — jumps directly to the "LLM Providers"
settings sub-page.
- **See Docs** — opens `https://zed.dev/docs/ai/llm-providers`.

Also adds `IconButton::hoverable_tooltip`, mirroring the existing
`.tooltip(...)` forwarding, since `IconButton` didn't previously expose
the underlying `ButtonLike::hoverable_tooltip` capability needed for
interactive tooltip content.

Release Notes:

- Improved the commit message tooltip to link directly to LLM provider
settings and documentation when no provider is configured.

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>