refactor: power-confirm via PowerAction table (v0.6.14)

Align the power-confirm flow to moonset's ActionDef pattern, in lockstep
with moongreet: a PowerAction table + create_power_button factory replace
the two hand-wired reboot/shutdown handlers and the loose-param
show_power_confirm. Add an in-flight re-trigger guard
(power_box.set_sensitive(false)) and clear a stale error_label when
showing a new prompt.

DECISIONS.md

@@ -2,6 +2,13 @@
 
 Architectural and design decisions for Moonlock, in reverse chronological order.
 
+## 2026-06-02 – Align power-confirm to moonset's ActionDef pattern (v0.6.14)
+
+- **Who**: ClaudeCode, Dom
+- **Why**: A code review of moongreet's power-confirm (ported from this file) flagged the shared pattern as lower-altitude than moonset's: two near-identical reboot/shutdown handlers and a `show_power_confirm` taking loose `message`/`action_fn`/`error_message` params that can drift apart. moonset already solved this with an `ActionDef` table + button factory. Changed here in lockstep with moongreet to keep the three projects symmetric.
+- **Tradeoffs**: A `PowerAction` struct + `power_actions()` table + `create_power_button` factory is slightly more machinery for two actions, but couples icon/prompt/error/action into one value (a mismatched prompt/action becomes unrepresentable) and makes a third action a one-line table entry. Did NOT touch `confirm_box: Rc<RefCell<Option<gtk::Box>>>` — moonset uses the same, it is the shared convention.
+- **How**: Replaced the two hand-wired handlers with a loop over `power_actions()`; `show_power_confirm`/`execute_power_action` now take `PowerAction` (Copy) instead of three loose strings. Added an in-flight re-trigger guard via `power_box.set_sensitive(false)` (re-enabled on failure), matching moonset; also clear a stale `error_label` when showing a new prompt.
+
 ## 2026-05-04 – Drop PAM account/session stack, remove `check_account`, drop `pam_acct_mgmt` from password path (v0.6.13)
 
 - **Who**: ClaudeCode, Dom