refactor: remove headless mode

Headless mode was half-built and untested. Agent-loop is a plugin
that runs interactively via tmux — there's no CI use case yet.
Removes --headless flag, timeout compatibility shim, output capture
logic, and LOOP_AGENT_TMPFILE handling. Cuts 82 lines from loop.sh.

README.md

@@ -72,20 +72,6 @@ Or ask Claude Code "status" — it reads `.loop/prd.json` and `.loop/progress.md
 
 Each generator and evaluator run is a full Claude Code session saved to history. Use `claude -r` to resume any session and inspect what happened, debug a rejection, or continue from where it left off.
 
-## Headless Mode
-
-For CI or background execution without the interactive UI:
-
-```bash
-.loop/loop.sh --headless [options]
-
---headless                       Run without interactive UI
---mode <implement|explore|fix>   Operating mode
---max <N>                        Maximum iterations (default: 20)
---skip-eval                      Skip evaluator pass
---dry-run                        Print assembled prompts without running
-```
-
 ## Architecture
 
 ### Generator