Support `brew install ccrouter` via Homebrew tap

[guo]

Description

Add Homebrew install support so macOS/Linux users can brew install ccrouter
instead of using the curl one-liner or building from source.

Context

Current install paths:

• curl -fsSL .../install.sh | sh
• manual binary download from Releases
• cargo build --release

Homebrew is the dominant package manager on macOS and widely used on Linux,
and we already publish prebuilt release binaries for both macOS (universal)
and Linux (x86_64-musl, aarch64-musl), which is exactly what a Homebrew
formula needs.

Recommended approach: a tap repo (e.g. guo/homebrew-ccrouter) with a
formula that downloads the matching release tarball and installs the binary.
This keeps the formula off homebrew-core (which has its own review burden)
while still giving users a clean brew tap guo/ccrouter && brew install ccrouter flow.

The release workflow already produces the artifacts the formula will reference.
We'll need to either hand-update the formula's url + sha256 per release,
or add a CI step that bumps the tap automatically on each tag.

Acceptance criteria

• homebrew-ccrouter tap repo created
• Formula installs the correct binary for macOS arm64/x86_64 and Linux x86_64/aarch64
• brew install guo/ccrouter/ccrouter works end-to-end
• README install section updated with the brew instructions
• (Optional) Release workflow auto-bumps the formula on new tags