docs: user-chosen boost duration; CWU limit 50 °C

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/spec.md

@@ -59,11 +59,11 @@ Functional:
   pumps, heater, alarm), current targets and temperatures, shown simply for my parents.
 - F2 History for the last 7 days.
 - F3 Change the four setpoints, nothing else for now: economy and comfort temperature of CWU
-  (4143, 4144) and CO (4131, 4132). The user picks any value within allowed limits, or one tap
-  on a named preset. Limits and presets live in the backend config (limits never wider than the
-  controller's ranges: CO 5–35 °C, CWU 5–70 °C). Typical uses, as my father does today:
-  - **Boost**: raise the economy temperature to heat outside the weekly program, for a chosen
-    time; the previous value is restored automatically.
+  (4143, 4144) and CO (4131, 4132). The user picks the value, or one tap on a named preset.
+  Limits and presets live in the backend config: CWU 5–50 °C (the heat pump's maximum, confirmed
+  by my father; more would need the electric heater), CO 5–25 °C. Typical uses, as my father does today:
+  - **Boost**: raise the economy temperature to heat outside the weekly program, for a duration
+    the user picks (presets suggest one); the previous value is restored automatically.
   - **Away / not needed**: lower the comfort temperature (e.g. CWU 10 °C, CO 15 °C) until changed back.
 - F4 Alarms shown in the app, with notification on a new alarm.
 - F5 Health of backend, controller link and tunnel.