fix(update-notice): suggest brew upgrade for Homebrew installs

[erikengervall]

The startup update notice always tells people to run npm install -g firecrawl-cli. For a Homebrew install that is the wrong fix: it installs a second copy through npm and leaves the brew keg stale.

What changed

• updateCommand() in src/utils/update-notice.ts picks the upgrade command from where the CLI is installed. When the module lives under a Homebrew keg (.../Cellar/firecrawl-cli/...), the notice says brew upgrade firecrawl-cli; every other install keeps npm install -g firecrawl-cli. It reads __dirname, which Node resolves through the bin symlink, so /opt/homebrew/bin/firecrawl maps to the Cellar path. A plain npm install -g with Homebrew's Node lives in /opt/homebrew/lib/node_modules and still gets the npm hint.
• formatUpdateNotice and the shared colorizeUpdateNotice take the chosen command, and maybeShowUpdateNotice accepts an installPaths override for tests.
• Removes the old homebrew/firecrawl-cli.rb draft. It was pinned to 1.10.0 with placeholder checksums and was never installable; a tap formula built from the npm tarball replaces it.

detectPackageManager is unchanged, so firecrawl init behaves as before.

Testing

• New unit tests cover the macOS and Linux Cellar paths, a Homebrew-Node npm global path, and the full notice under a Cellar install.
• Packed this branch, installed it into a Homebrew-style keg (Cellar/firecrawl-cli/1.26.9/libexec, linked from a bin/ symlink), and ran firecrawl status in a TTY with a cached newer version. The notice printed Run brew upgrade firecrawl-cli to update.; the same package under a plain npm global prefix printed the npm command.
• pnpm run type-check, pnpm run format:check and pnpm run build pass. The one failing test in a full local run (parse.test.ts, "without auth ... no key") also fails on main when FIRECRAWL_API_KEY is set in the shell, so it is unrelated.

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Summary by cubic

Fixes the startup update notice so Homebrew installs are told to run brew upgrade firecrawl-cli instead of npm install -g firecrawl-cli, which previously installed a second copy through npm and left the brew keg stale.

• Detects a Homebrew install by checking whether the module lives under a Cellar keg path or, for compiled binaries, whether the executable path points into one; all other installs keep the npm hint.
• Removes the draft homebrew/firecrawl-cli.rb formula, which was pinned to 1.10.0 with placeholder checksums and was never installable.

^{Written for commit 2967425. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Shadow auto-approve: would not auto-approve because issues were found.

View guided diff | Turn on auto-fix | Re-trigger cubic</sub>

[cubic-dev-ai]

0 issues found across 2 files (changes from recent commits).

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Shadow auto-approve: would auto-approve. Update notice now suggests brew upgrade only for Homebrew Cellar installs, keeping the npm hint elsewhere; adds tests and removes an uninstallable placeholder Homebrew formula. Bounded, clearly beneficial fix to incorrect update guidance.

View guided diff | Turn on auto-fix | Re-trigger cubic</sub>