fix: show Command Bank in main pos menu; fix pos bank run crash

- bin/pos: _pos_category_list now emits category-less tools (pos-bank,
  pos-config, pos-tree) as sorted menu entries with an empty subcommand
  column, deduped against real categories (pos-ai). bank previously
  never appeared in the bare 'pos' menu.
- bin/pos-bank: fixed invalid 'local name="" -a cli_params=()' at
  cmd_run (line 150) — bash rejected '-a' after an assignment, crashing
  every 'pos bank run' with 'local: -a: not a valid identifier'.
  Split into 'local name=""' + 'local -a cli_params=()'.
- tests/t-bank.sh: added B12-B14 covering cmd_run (no-params,
  missing-command, param substitution) — would have caught the crash.
- AGENT_TODO.md: bank feature moved to Done.

bin/pos-bank

@@ -147,7 +147,8 @@ cmd_show() {
 
 # ── cmd_run ──────────────────────────────────────────────────────
 cmd_run() {
-    local name="" -a cli_params=()
+    local name=""
+    local -a cli_params=()
     if [ $# -eq 0 ]; then
         name="$(_pick_command)" || return 0
     else