feat(build): add multi-platform release targets, Homebrew formula, and INSTALL.md

Taskfile:
- Add build-linux-arm64, build-darwin-amd64, build-darwin-arm64 targets
- Rename build-linux to build-linux-amd64 (keep build-linux alias)
- Rename Windows output to glint-<tag>-windows-amd64.exe for consistency
- Add build-release task that builds all five platforms in one shot

Formula/glint.rb:
- Homebrew source-build formula; depends_on "go" => :build
- tap: brew tap k3nny/glint https://github.com/k3nny/homebrew-glint
- Includes basic test block (--version + lint a trivial pipeline)

INSTALL.md:
- Pre-built binary download instructions for all five platforms
- Homebrew tap setup and formula update procedure
- go install one-liner
- Link to README integrations section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

INSTALL.md

@@ -0,0 +1,139 @@
+# Installing glint
+
+## Requirements
+
+- Go 1.21 or later (for building from source)
+- Any 64-bit Linux, macOS, or Windows system (for pre-built binaries)
+
+---
+
+## Option 1 — Build from source
+
+```bash
+git clone https://git.k3nny.fr/k3nny/glint
+cd glint
+go build -o glint ./cmd/glint/...
+sudo mv glint /usr/local/bin/
+```
+
+Or with [Task](https://taskfile.dev):
+
+```bash
+task build
+sudo mv glint /usr/local/bin/
+```
+
+---
+
+## Option 2 — Download a pre-built binary
+
+Pre-built binaries are attached to each [release](https://git.k3nny.fr/k3nny/glint/releases).
+
+| Platform | File |
+|----------|------|
+| Linux x86-64 | `glint-vX.Y.Z-linux-amd64` |
+| Linux ARM64 | `glint-vX.Y.Z-linux-arm64` |
+| macOS Intel | `glint-vX.Y.Z-darwin-amd64` |
+| macOS Apple Silicon | `glint-vX.Y.Z-darwin-arm64` |
+| Windows x86-64 | `glint-vX.Y.Z-windows-amd64.exe` |
+
+### Linux (amd64)
+
+```bash
+VERSION=v0.3.1
+curl -Lo glint https://git.k3nny.fr/k3nny/glint/releases/download/${VERSION}/glint-${VERSION}-linux-amd64
+chmod +x glint
+sudo mv glint /usr/local/bin/
+```
+
+### Linux (ARM64 — Raspberry Pi 4, AWS Graviton, …)
+
+```bash
+VERSION=v0.3.1
+curl -Lo glint https://git.k3nny.fr/k3nny/glint/releases/download/${VERSION}/glint-${VERSION}-linux-arm64
+chmod +x glint
+sudo mv glint /usr/local/bin/
+```
+
+### macOS (Apple Silicon — M1/M2/M3)
+
+```bash
+VERSION=v0.3.1
+curl -Lo glint https://git.k3nny.fr/k3nny/glint/releases/download/${VERSION}/glint-${VERSION}-darwin-arm64
+chmod +x glint
+sudo mv glint /usr/local/bin/
+```
+
+### macOS (Intel)
+
+```bash
+VERSION=v0.3.1
+curl -Lo glint https://git.k3nny.fr/k3nny/glint/releases/download/${VERSION}/glint-${VERSION}-darwin-amd64
+chmod +x glint
+sudo mv glint /usr/local/bin/
+```
+
+### Verify the installation
+
+```bash
+glint --version
+```
+
+---
+
+## Option 3 — Homebrew (macOS and Linux)
+
+A Homebrew tap is available at `k3nny/glint`.
+
+> **First-time setup:** create a GitHub repository named `homebrew-glint`
+> under your account and copy [`Formula/glint.rb`](Formula/glint.rb) into it.
+> Users then install via the tap as shown below.
+
+```bash
+brew tap k3nny/glint https://github.com/k3nny/homebrew-glint
+brew install glint
+```
+
+To upgrade:
+
+```bash
+brew upgrade glint
+```
+
+The formula builds glint from source using Go, which Homebrew provides
+automatically as a build dependency. No pre-built binary download is needed.
+
+### Updating the formula on a new release
+
+After tagging a new release, update `Formula/glint.rb`:
+
+1. Compute the tarball checksum:
+   ```bash
+   curl -sL https://git.k3nny.fr/k3nny/glint/archive/vX.Y.Z.tar.gz | sha256sum
+   ```
+2. Update `url` and `sha256` in the formula.
+3. Commit and push to `homebrew-glint`.
+
+---
+
+## Option 4 — Go install
+
+If you already have Go 1.21+:
+
+```bash
+go install git.k3nny.fr/k3nny/glint/cmd/glint@latest
+```
+
+The binary is placed in `$(go env GOPATH)/bin/`. Add that directory to your
+`PATH` if it is not already there:
+
+```bash
+export PATH="$PATH:$(go env GOPATH)/bin"
+```
+
+---
+
+## Integrations
+
+For editor and CI integrations (pre-commit hook, GitLab CI component, GitHub
+Actions, VS Code extension) see [README.md](README.md#integrations).