feat: AI command prompt - run or edit detected shell commands

- _extract_commands() parses bash/sh/shell fenced code blocks
- _prompt_run_command() prompts [Y/n] via /dev/tty after AI response
- Y/Enter: execute via run helper (respects DRY_RUN)
- n: command added to history (press up-arrow to recall, edit, run)
- Integrated in both cmd_ask() and cmd_chat()
- Skipped when output is piped/redirected

DOC/AGENT_Context_Project.md

@@ -633,7 +633,7 @@ Use conventional prefixes: `feat:`, `fix:`, `docs:`, `refactor:`, `chore:`
 | `bin/pos-system-health` | 209 | Host health dashboard (disk, RAM, services, backup age, fail2ban, docker); exit 1 if any FAIL |
 | `bin/pos-system-schedule` | 151 | Scheduled jobs: run a command on a timer; notify on threshold/change/error/always or silently |
 | `bin/pos-system-uninstall` | 415 | Remove pos toolkit binaries, services, shell integration, config, and data |
-| `bin/pos-ai` | 632 | AI assistant: ask, chat, sessions, capture, models, providers |
+| `bin/pos-ai` | 680 | AI assistant: ask, chat, sessions, capture, models, providers |
 | `bin/pos-config` | 80 | Interactive editor for the tools' runtime config (reads # POS_CONFIG: registry) |
 | `bin/pos-tree` | 112 | Show the pos CLI command tree: categories, commands, and subcommands |
 | `completions/pos.bash` | 306 | Dynamic bash completion |