repl: pre/post CMD hooks via config.hooks (closes #3)

Optional shell scripts trigger around every CMD: execution. Use cases:
audit logging, auto-format-after-edit, custom safety gates beyond the
existing confirm_cmd boolean.

Config shape:

    hooks = {
        pre_cmd  = "/path/to/pre-script",
        post_cmd = "/path/to/post-script",
    }

Contract per hook invocation:
  - The command line is piped to the hook on stdin.
  - Env vars: AISH_CMD (the command), AISH_TURN (#ctx.turns at the
    moment of dispatch), AISH_CWD (libc.getcwd() result).
  - Hook stdout is streamed live to the terminal via executor.exec
    (so the user sees its output regardless of exit status).

Pre-hook: non-zero exit aborts the command and emits a status line
including the exit code. last_exec_code is set to the hook's exit
so the {last_status} prompt template variable reflects the abort.

Post-hook: exit code is ignored (the spec says so); only the visible
stdout matters. Runs after the command's exec_end frame.

Tested with success, abort, and stdin-matches-env paths.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

config.lua

@@ -61,6 +61,16 @@ return {
         dir = (os.getenv("HOME") or ".") .. "/.local/share/aish",
     },
 
+    -- Issue #3: pre/post CMD hooks. Optional shell scripts triggered around
+    -- every CMD: execution. Each hook receives the command on stdin and
+    -- AISH_CMD / AISH_TURN / AISH_CWD as env vars. Non-zero exit on pre_cmd
+    -- aborts execution; post_cmd's exit code is ignored but its stdout is
+    -- logged. Default off (no hooks). Uncomment to enable.
+    -- hooks = {
+    --     pre_cmd  = (os.getenv("HOME") or ".") .. "/.aish/hooks/pre-cmd",
+    --     post_cmd = (os.getenv("HOME") or ".") .. "/.aish/hooks/post-cmd",
+    -- },
+
     -- Phase 2 (docs/PHASE2.md): MCP server registry + tool-call policy.
     -- The block is OFF by default — connect-at-startup happens only when
     -- `servers` is non-empty. Uncomment + adjust per your fleet.