feat: enable full install defaults

[OneNoted]

Summary

• enable cuda, local-rewrite, and osd in the default feature set so cargo install whispers builds the full local path by default
• update install docs to make the simple install command the full-featured path and document opt-out variants
• refresh requirements and notes to match the new default behavior

Testing

• cargo install --path . --locked --force

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: b0eca67b63

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Keep CUDA out of the default feature set

Changing default to include cuda makes every plain cargo test, cargo clippy, and cargo install whispers attempt a CUDA build. In this repo, the default-feature CI job runs cargo clippy/cargo test without installing CUDA (.github/workflows/ci.yml lines 33-36), and CUDA checks are separately gated on nvcc availability (lines 67-73), so this introduces immediate failures on non-CUDA runners and on user machines without the CUDA toolkit unless they know to override defaults.

Useful? React with 👍 / 👎.