docs: expand with-watch documentation

[kdy1]

Summary

• expand the internal with-watch contract docs to better document command modes, inference boundaries, rerun behavior, and release/install guarantees
• turn the crate README into a more complete user guide with quick start, troubleshooting, and shell limitation guidance
• add a public with-watch Mintlify page and wire it into the public docs navigation and overview pages

Testing

• cargo run -p with-watch -- --help
• pnpm --filter public-docs test

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Add Unix-only caveat for --shell usage

This section describes --shell support as if it is generally available, but the CLI explicitly errors on non-Unix systems (WithWatchError::ShellExecutionUnsupportedPlatform in crates/with-watch/src/error.rs). As written, Windows users following the new public quick-start/shell guidance will hit an immediate runtime failure, so this page should explicitly state the Unix-only platform boundary (matching the crate README).

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