Add trip mode: self-learning EV charging scheduler

User enters car SOC + departure deadline; EMS computes when to start
charging and activates the wallbox at the right time (grid import OK
for trip mode). Charging rate is learned from completed PM sessions,
improving over time. Car profiles (Mini Cooper SE 50 kWh, BMW ix2 63
kWh) are config-driven and selectable per trip.

- internal/trip/trip.go: Goal/Session types, Manager with per-cycle
  Tick() that accumulates energy, detects session completion, learns
  avg charge rate from JSONL session log
- internal/config: CarProfile + Cars map, TripGoalFile, SessionLogFile
- internal/status: trip card (active goal) + trip form (set new goal),
  CarOption list, formatDay/formatDur helpers
- main.go: tripMgr lifecycle, /trip + /trip/cancel HTTP handlers,
  runCycle integration (ShouldStartNow → ApplyOverride, auto-clear)
- configs/ems-config.yaml: cars section, trip_goal_file, session_log_file

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

configs/ems-config.yaml

@@ -112,3 +112,14 @@ ems:
   override_timeout: "1h"             # default lockout when EMS detects external Shelly change
   override_max_import_w: 800         # cancel override immediately if importing more than this (0 = disabled)
   monitor_only_file: "/etc/ems/monitor-only"  # presence of this file = monitor-only mode active
+  trip_goal_file: "/var/lib/ems/trip-goal.json"     # persisted active trip goal
+  session_log_file: "/var/lib/ems/sessions.jsonl"   # JSONL log of completed charge sessions
+
+# Known car profiles for trip mode
+cars:
+  mini:
+    name: "Mini Cooper SE"
+    battery_kwh: 50.0
+  bmw:
+    name: "BMW ix2 eDrive20"
+    battery_kwh: 63.0