feat(optimization): deadlines for consumers and EV, graded grid export

Three related scheduling improvements, all opt-in and behaviour-preserving
when the new fields are not set.

Flexible consumers get absolute time bounds next to the recurring
time_windows: earliest_start_datetime and deadline_datetime, where the
deadline requires the complete run to have *finished* before that moment
("clean dishes by 03:00 tonight"). When no start can meet it,
deadline_policy decides between BEST_EFFORT (run as early as possible, so
the delay rather than the cost is minimized) and STRICT (keep the
deadline; a ONCE consumer then fails the optimization). The solution
reports appliance_deadline_missed per device.

The EV charging target can be given the same kind of deadline, as an
absolute min_soc_deadline_datetime and/or a relative min_soc_max_duration_h
("full in 6 hours"), the earlier of the two winning. The ev_soc_miss
penalty is then evaluated at that slot instead of at the end of the
horizon, and the seeding heuristic only proposes charge slots before it.

Battery-to-grid export under direct marketing is no longer all-or-nothing:
grid_export_rates configures the selectable export levels as a factor of
the rated discharge power (default [0.25, 0.5, 0.75, 1.0]). Each rate is
its own optimizer state, with the full-power state keeping its previous
index so existing seeds and heuristics are unaffected. The chosen level
per slot is reported in battery_grid_export_factor and as the
GRID_SUPPORT_EXPORT operation factor.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/_generated/configexample.md

@@ -58,6 +58,12 @@
                        0.9,
                        1.0
                    ],
+                   "grid_export_rates": [
+                       0.25,
+                       0.5,
+                       0.75,
+                       1.0
+                   ],
                    "min_soc_percentage": 0,
                    "max_soc_percentage": 100
                }
@@ -85,6 +91,12 @@
                        0.9,
                        1.0
                    ],
+                   "grid_export_rates": [
+                       0.25,
+                       0.5,
+                       0.75,
+                       1.0
+                   ],
                    "min_soc_percentage": 0,
                    "max_soc_percentage": 100
                }