Replace fatih/color with in-tree ANSI helpers

[pietern]

Summary

• Drops github.com/fatih/color as a direct dependency by migrating its ~14 call sites (bundle render, bundle run, cfgpickers, logstream, cmd/labs, experimental/aitools, experimental/ssh, python_mutator) to a small ANSI helper set.
• Adds libs/cmdio/color.go with cmdio.Red(ctx, msg)-style helpers and a RenderFuncMap(ctx) for templates. The gate matches fatih/color's historical stdout-TTY decision and degrades to plain text when ctx has no cmdIO attached.
• Stacks on top of Replace nwidger/jsoncolor with an in-tree colorizer #5170. ANSI constants shared across both colorizers now live in libs/cmdio/color.go.

No user-visible output changes — the new helpers emit byte-identical SGR sequences.

Test plan

• Manual smoke: databricks bundle validate against a bundle with errors and warnings (colored summary on TTY, uncolored when piped) and databricks current-user me -o json (colored on TTY, uncolored when piped through jq).

This pull request and its description were written by Isaac.

[simonfaltum]

LGTM