feat(cluster): persist learnt locators behind a "Chase new grids" option

The callsign->grid map died with the process. Every restart began with an empty
Locator column that took an hour of listening to refill, and everything learnt
the day before was thrown away.

internal/gridcache is its own SQLite file in the data directory, not a table in
the settings database: that one sits wherever the operator chose to put it,
often a synchronised folder, and a store that rewrites itself every minute has
no business there. Deleting the file costs a few days of listening and nothing
else.

Callsign is the primary key and the newest report wins — operators move, go
portable, go on expedition, and a stale locator is worse than none for grid
chasing because it reads as a square already worked. Entries not seen in two
years are pruned at open: that is the one way this cache can be actively wrong
rather than merely empty, and it is what bounds a store that would otherwise
only grow.

Only CHANGES are queued. The feeds repeat themselves, so writing every report
would put the whole stream in the batch instead of the news in it. Batches
flush on a timer and on shutdown — a restart is exactly when the cache is worth
the most.

Rotation is switched off while the store is attached: the cap would discard
callsigns the database still holds and the lookup would then miss what we know.
Age in the store is the bound instead.

frontend/wailsjs/go/main/App.d.ts

@@ -404,6 +404,8 @@ export function GetCatalogCodes():Promise<Array<string>>;
 
 export function GetChangelog():Promise<Array<main.ChangelogEntry>>;
 
+export function GetChaseNewGrids():Promise<boolean>;
+
 export function GetChatHistory(arg1:number):Promise<Array<main.ChatMessage>>;
 
 export function GetClublogCtyInfo():Promise<main.ClublogCtyInfo>;
@@ -970,6 +972,8 @@ export function SetCIVTrace(arg1:boolean):Promise<void>;
 
 export function SetCWDecoderPitch(arg1:number):Promise<void>;
 
+export function SetChaseNewGrids(arg1:boolean):Promise<void>;
+
 export function SetClublogCtyEnabled(arg1:boolean):Promise<void>;
 
 export function SetClublogMostWantedEnabled(arg1:boolean):Promise<void>;

frontend/wailsjs/go/main/App.js

@@ -750,6 +750,10 @@ export function GetChangelog() {
   return window['go']['main']['App']['GetChangelog']();
 }
 
+export function GetChaseNewGrids() {
+  return window['go']['main']['App']['GetChaseNewGrids']();
+}
+
 export function GetChatHistory(arg1) {
   return window['go']['main']['App']['GetChatHistory'](arg1);
 }
@@ -1882,6 +1886,10 @@ export function SetCWDecoderPitch(arg1) {
   return window['go']['main']['App']['SetCWDecoderPitch'](arg1);
 }
 
+export function SetChaseNewGrids(arg1) {
+  return window['go']['main']['App']['SetChaseNewGrids'](arg1);
+}
+
 export function SetClublogCtyEnabled(arg1) {
   return window['go']['main']['App']['SetClublogCtyEnabled'](arg1);
 }