Create terminal scenes (litmus-yx5o)

Create realistic terminal scenes: shell prompt, ls –color, git diff (with context/additions/deletions/merge conflicts), delta output, tig log view.

Summary of Changes

Added scenes module with 5 built-in terminal scenes:

Shell prompt: prompts with grep output, error messages, and dirty branch indicator
Git diff: multi-hunk diff with context/additions/deletions
Directory listing: colorized ls -la with dirs, executables, symlinks, hidden files
Cargo build: compiler warnings, errors with code spans, notes, and help suggestions
Git log: branch graph with commit hashes, HEAD/remote decorations, branch names