feat: auto-detect color output in CI environments

[vmaerten]

Summary

fixes #1589

Running Task in CI often produces monochrome output, making it harder to scan logs and spot important information. This PR fixes that.

Task now automatically enables colored output when running in CI environments (CI=true). This matches the behavior of popular tools like Terraform, cargo, npm, and pytest which all auto-detect CI and enable colors.

Before

task: [build] go build -o ./bin/task ./cmd/task
task: [test] go test ./...
task: Failed to run task "test": exit status 1

Plain text wall - errors blend in with everything else.

After

Colored output with visual hierarchy - task names in green, errors in red, making logs scannable at a glance.

Why this matters

• Improved readability - Colors help distinguish task names, commands, and errors
• Industry standard - Tools like Terraform, cargo, npm already do this
• GitHub Actions supports ANSI colors - No reason not to use them
• Zero configuration - Just works, respects NO_COLOR if needed

Changes

• Auto-detect CI via CI=true environment variable
• Add color option to .taskrc.yml for global configuration
• Respect priority: CLI flag > taskrc > NO_COLOR > FORCE_COLOR > CI > TTY default
• Update documentation and JSON schema

Test plan

• CI=true task --list shows colored output
• NO_COLOR=1 CI=true task --list has no colors (NO_COLOR takes priority)
• task --color=false disables colors even with CI=true
• Setting color: false in ~/.taskrc.yml disables colors globally