Unify band-opportunity logic and add B+/a/o status to the station table

Issue #70, #66, #65

Introduces a shared BandOpportunityResolver so the station table's band
columns, the New bands filter, the band-upgrade hint, the priority
score, the map markers and the automatic reachability band selection
all derive band availability the same way: recent QRG detections (30
min window) plus station-name hints, evaluated across every active
callsignRaw variant, with manual NOT-QRV always taking precedence.

The per-band table cells now distinguish:
- X: worked on this band
- a: band available, call not worked on any band yet
- B+: band available, call already worked on another band
- o: grid square already worked on this band (any station) - combines
  with the others, e.g. "ao" or "B+o"

Both "a" and "o" can be toggled off in the GUI settings tab.

Assisted by Claude Sonnet 5 <noreply@anthropic.com>

pom.xml

@@ -153,7 +153,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <version>5.12.2</version>
+            <version>${junit.version}</version>
             <scope>compile</scope>
         </dependency>
         <dependency>
@@ -266,6 +266,15 @@
                 <version>${maven.surfire.plugin}</version>
                 <configuration>
                     <testFailureIgnore>true</testFailureIgnore>
+                    <!--
+                        Without this, Surefire's automatic module-path detection splits the
+                        JUnit Platform jars across classpath and module-path inconsistently
+                        (module org.junit.platform.commons ends up loaded while a class from
+                        junit-platform-engine stays in the unnamed module), which fails with
+                        an IllegalAccessError before any test can run. The project itself has
+                        no module-info.java, so plain classpath execution is correct here.
+                    -->
+                    <useModulePath>false</useModulePath>
                 </configuration>
             </plugin>