feat(aprs): pick a map symbol from a list instead of typing two characters

The symbol table and code were free-text fields with no validation and no hint. Only the
first character was ever used, and only at packet-build time, so an operator could type
"satellite" into the table field, watch it persist, and beacon as "/" - the field lied about
what it did. aprs.fi's troubleshooting guidance puts transmit-side symbol misconfiguration
among the first things to check when a station never appears correctly.

The single strongest argument for a list: \S is Satellite/Pacsat but /S is SHUTTLE. One
keystroke apart, and both look right to someone typing from memory.

Fourteen entries covering fixed, on-foot, field, four vehicle classes, satellite, yagi,
phone, internet-only and handheld. Renderings are from aprs.org/symbols/symbolsX.txt
(WB4APR, Nov 2015) rather than recalled. A symbol the operator already set that is not on
the list appears first in the menu and stays selected, so opening the picker cannot silently
change an existing station's appearance.

The default changes from "/>" (CAR) to "/-" (House). The old default's own comment conceded
it was "a reasonable stand-in for a phone", but it showed every non-driving operator as a
vehicle. A house is right for most users and obviously wrong rather than misleading for the
rest. This cannot disturb an existing install: saveConfig writes every key unconditionally
and the enable switch calls it, so anyone who has ever turned APRS on has both symbol keys
on disk and the changed fallbacks cannot reach them. All three sites move together -
AprsStore's load fallback, AprsCard's blank-field fallback, and AprsBeacon.DEFAULT_SYMBOL -
because leaving one behind would substitute a car whenever the stored code was unusable.

The list lives in core:domain as pure data holding resource names rather than text, so the
wording stays in the locale files. Tests assert that every entry survives the transmit
sanitiser, that the pairs and description keys are unique, and that a pair off the list
reports as absent rather than resolving to something near it.

core/data/src/main/java/com/rtbishop/look4sat/core/data/aprs/AprsStore.kt

@@ -24,6 +24,15 @@ object AprsStore {
     private const val KEY_STATUS = "status"
     private const val KEY_SYMBOL_TABLE = "symbol_table"
     private const val KEY_SYMBOL_CODE = "symbol_code"
+
+    /**
+     * A house, not a car.
+     *
+     * Only fresh installs see this: saveConfig writes every key unconditionally and the enable
+     * switch calls it, so anyone who has ever turned APRS on has both symbol keys on disk and this
+     * fallback cannot reach them.
+     */
+    private const val DEFAULT_SYMBOL_CODE = "-"
     private const val KEY_LAST_TIME = "last_report_time"
     private const val KEY_LAST_OK = "last_report_ok"
     private const val KEY_LAST_DETAIL = "last_report_detail"
@@ -41,7 +50,7 @@ object AprsStore {
             intervalMin = p.getInt(KEY_INTERVAL, 5),
             statusText = p.getString(KEY_STATUS, "Look4Sat APRS") ?: "Look4Sat APRS",
             symbolTable = p.getString(KEY_SYMBOL_TABLE, "/") ?: "/",
-            symbolCode = p.getString(KEY_SYMBOL_CODE, ">") ?: ">"
+            symbolCode = p.getString(KEY_SYMBOL_CODE, DEFAULT_SYMBOL_CODE) ?: DEFAULT_SYMBOL_CODE
         )
     }