feat(alerts): fire_on_phase_skip backstop + public FSM lockout API

When the FSM observes ARMED → light_{green,red} directly (the dark
prime was missed), the color classifier likely mis-labeled the dark
phase as gray/background. Missing a fire is worse than a noisy alert,
so the new [options.alerts] fire_on_phase_skip flag (default True)
emits a phase_skip_fire alert on that transition with the standard
240s lockout to dedupe detector bounces.

Adds public StateMachine.is_locked / record_fire so the handler does
not reach into private attrs. _handle_tick now accepts an optional
cfg to read the flag; falls back to True if cfg is absent (tests).

Config gains AlertBehaviorCfg (new alerts field), parsed from
[options.alerts]. Example TOML updated with an explanatory comment.

Tests: test_phase_skip_fire_when_flag_on,
test_phase_skip_no_fire_when_flag_off,
test_phase_skip_lockout_suppresses_spam,
test_state_machine_is_locked_and_record_fire_public_api.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

configs/example.toml

@@ -81,6 +81,13 @@ low_conf_run = 3
 phaseb_timeout_s = 600
 dead_letter_path = "logs/dead_letter.jsonl"
 
+# Alert-behavior toggles (not screenshot-attachment; see attach_screenshots below).
+# fire_on_phase_skip: emit a backstop "PHASE SKIP" alert when the FSM observes
+# ARMED → light_green/light_red directly (skipping the dark prime). Default on
+# because missing a fire is worse than a false-positive phase-skip alert.
+[options.alerts]
+fire_on_phase_skip = true
+
 # Per-kind screenshot-attach toggles. All default to true on upgrade.
 # Accepts either a bare bool (legacy: attach_screenshots = true) or this table.
 [options.attach_screenshots]