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>

docs/PROJECT_CONTEXT.md

@@ -145,6 +145,7 @@ CR/LF framing, XML framing, ports/transports, callsign normalization and frequen
 - The active terrain profile provider is Open-Meteo using Copernicus GLO-90 data.
 - The terrain profile cache lives in its own global database `~/.praktiKST/terrainprofilecache.db`. It is deliberately not part of an operator profile: terrain profiles are pure geometry derived from two locators and a sample count, and at a multi operator station both operators share one location, so a per-profile copy would only double the traffic against the terrain service.
 - Cached entries are separated by owner identity through the primary key (`owner_callsign_raw` + `owner_locator6`). Earlier versions stored a single owner identity in a meta table and dropped the whole cache whenever the configured callsign or locator changed; with several operator profiles that would discard every computed profile on each switch. The old `TerrainProfileCache*` tables inside `praktiKST.db` are left in place and are still readable by older releases; the new file starts empty and refills itself.
+- The highest point of a remote locator square (path analysis, Station tab switch, on by default) is found by `LocatorHighestPointResolver`: a 5 x 5 grid of cell centres, one batched request against the same Open-Meteo provider and rate limiter as the profile, cached in memory per locator for the session and not persisted. A failed lookup is retried after five minutes; until then the analysis falls back to the square centre and that result is not kept in the reachability cache. The lookup runs on the reachability thread only; request building peeks the cache without blocking. The optional own ground height ASL replaces the first profile sample's elevation, a resolved highest point the last one.
 - `OfflineDemImportService` only prepares a local directory and copies manually selected Copernicus GLO-30 GeoTIFF files into it. Importing files does not activate an offline provider or change the active calculation chain.
 
 ### ON4KST session and authentication