Path analysis: own ground height ASL and highest point of the remote locator square (#133)

* Path analysis: own ground height ASL and highest point of the remote square

Two new settings in the path-analysis section of the Station tab:

- Own ground height ASL (stn_pathAnalysisOwnHeightAslMeters). Empty keeps
  the elevation model value at the own locator centre; a value from -500 to
  9000 m replaces the elevation of the first profile sample. The antenna
  height AGL is still added on top. The field commits on Enter or focus
  loss into the settings draft and reports a refused entry; it keeps the
  operator's spelling while that names the drafted number, because the
  draft is Compose state and would otherwise swap "25" for "25.0" under
  the cursor right after Enter.
- Target station on the highest point of its locator square
  (stn_pathAnalysisDxHighestPointInSquare, on by default). The remote square
  is sampled on a 5 x 5 grid of cell centres in one batched request against
  the Open-Meteo provider, the highest sample becomes the path end with its
  position and elevation. LocatorHighestPointResolver caches the result per
  locator for the session and backs off five minutes after a failure
  (failure list pruned and bounded); the analysis then falls back to the
  square centre and that result is not kept.

Both settings are drafted like the other path-analysis settings and take
effect with Apply/Close or Save; the reachability service reads the stored
values only.

The lookup runs on the reachability thread only. Building a request peeks
the resolver cache without blocking, so a cached square moves the endpoint
right away. The calculation key now includes the own height and the remote
ground elevation at full precision, and the switch, so changing either
recalculates.

Also assign the result of sanitizeEffectiveEarthRadiusFactor in the
PathAnalysisRequest constructor; it was called and dropped. No behaviour
change: the sanitizer is the identity for valid factors, and the analysis
service sanitizes again.

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

* Document own ground height and highest-point setting of the path analysis

Changelog v1.50 (New), configuration and features pages in English and
German, and the terrain section of PROJECT_CONTEXT.

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

app-desktop/src/main/i18n/strings_en.properties

@@ -115,6 +115,7 @@ station.callsign=Callsign
 station.chatSection=Chat category
 station.defaultsSection=Defaults
 station.demDirectory=DEM root directory
+station.invalidOwnHeightAsl="{0}" is not a valid height. Enter metres from -500 to 9000, or leave the field empty to use the elevation model.
 station.locator=Locator
 station.mainCategory=Main category
 station.maxQrb=Maximum QRB
@@ -122,6 +123,7 @@ station.nameMain=Name, main category
 station.nameSecond=Name, second category
 station.ownAntennaGain=Own antenna gain, dBi
 station.ownAntennaHeight=Own antenna height, metres
+station.ownHeightAsl=Own ground height ASL, metres
 station.ownSection=Own station
 station.ownTxPower=Own TX power, watts
 station.password=Password
@@ -137,6 +139,7 @@ station.serverHost=Server host name
 station.serverPort=Server port
 station.serverSection=ON4KST server
 station.targetAntennaGain=Target antenna gain, dBi
+station.targetHighestPoint=Target station on the highest point of its locator square
 station.targetTxPower=Target TX power, watts
 trxSynch.hint=An enabled source does not produce a frequency by itself. The own QRG is only updated once valid RadioInfo or Win-Test STATUS data actually arrives; until then it stays as entered by hand.
 trxSynch.hintSection=What an enabled source does