Add sensor freshness checks

ROADMAP.md

@@ -43,7 +43,7 @@ Current behavior: **shadow mode only**. `generic_thermostat` remains the one and
 - [ ] Add Home Assistant test harness coverage for initial setup, update, restart/reload, options changes, missing sensors, `heat/off`, target changes, teardown and uninstall.
 - [ ] Verify that **zero physical-device service calls** occur in observation mode, including restart and failed update cases.
 - [ ] Establish deterministic handling of 5-minute transitions, polling jitter, timestamp discontinuities, missing data and real switch transitions between samples.
-- [ ] Add input freshness thresholds and diagnostics that identify exactly which source is missing/stale/invalid.
+- [x] Add input freshness thresholds and diagnostics that identify exactly which source is missing/stale/invalid.
 - [ ] Verify that source switching, entity renaming, adding/removing rooms and replacing the relay do not silently reuse incompatible fitted coefficients.
 - [ ] Version persisted model schema; test corrupted/older state and migration/rollback behavior.
 - [ ] Verify calculated sample totals and successful/failed fitting counters; expose reasons why training/prediction is unavailable.
@@ -61,8 +61,9 @@ They are not a full HA test harness. Per-room accepted ON/OFF counts, additive
 payload schema v2, conservative relay-transition rejection, jitter normalization,
 Fahrenheit targets and forecast input-change guards are implemented.
 
-Next implement configurable freshness/alignment with diagnostics and a supported
-HA test harness/CI. Then improve event-based sampling and identity/persistence
+Configurable room/weather report-age limits and per-source quality diagnostics
+are now implemented with offline coverage. Sensor alignment remains open.
+Next implement a supported HA test harness/CI. Then improve event-based sampling and identity/persistence
 migration tests. Only after those reliability checks proceed to Milestone 1's
 recorded forecasts and walk-forward evaluation. Live control remains unauthorized.