A small subset of these devices shipped without the DPS310 sensor
because the part was discontinued by the manufacturer. Customers seeing
the DPS310 entities reporting "unknown" in Home Assistant have been
confused, so this expands and aligns the existing availability notes.

Changes:
- Add a new FAQ entry on each of AIR-1, MTR-1, MSR-2 that directly
  addresses "DPS310 shows unknown - is my device broken?"
- Add the availability note to MTR-1's DPS310 Temperature Offset and
  MSR-2's DPS Temperature Offset config entries (was missing; AIR-1
  already had it on its Pressure Offset).
- Add a DPS310 Pressure sensor entry to AIR-1 sensor-definitions
  (firmware exposes it but the wiki didn't document it).
- Convert the Homey AIR-1 and Homey MSR-2 sensor-definitions pages
  from stale full duplicates to --8<-- snippet wrappers of the main
  files, matching the MTR-1 Homey pattern. This also picks up the
  DPS310 availability notes on the Homey side automatically and fixes
  a wrong "psi" unit on the stale Homey AIR-1 copy.