Make the terrain profile cache multi operator safe

The cache stored a single owner identity in a meta table and dropped the whole
TerrainProfileCache table whenever the configured callsign or locator differed
from it. With several operator profiles that turns the cache into a permanent
miss: every switch between two operators with different locators would discard
every computed profile.

Entries are separated by owner identity through the primary key already, so the
wipe is replaced by an owner table that simply records which identities are in
use. A different owner now misses the cache instead of clearing everybody's.

The cache also moves out of the worked station database into its own global
terrainprofilecache.db. Terrain profiles are pure geometry derived from two
locators and a sample count; at a multi operator station both operators share
one location, so a per profile copy would only double the traffic against the
terrain service. No migration is needed, the new file refills itself, and the
old tables stay readable for older releases.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hpa6bjie5qkeNG62y6FmXm

github_docs/en-Configuration.md

@@ -948,6 +948,8 @@ Several operators sharing one computer need different callsigns, locators and la
 
 On Windows the same files live below `%USERPROFILE%\.praktiKST\`.
 
+Everything else stays shared: audio files, colour schemes, DEM and terrain packages, the terrain profile cache (`terrainprofilecache.db`), the error log and the version information.
+
 The **Default** profile keeps using exactly the files an existing installation already has. **Upgrading to v1.50 moves, copies and rewrites nothing.** Anyone reinstalling an older KST4Contest release finds their configuration and their worked stations unchanged.
 
 ### Shared or own worked stations