feat: split settings DB from the QSO logbook (own file per profile)

Design flaw: opslog.db held BOTH the config (settings + profiles) AND the SQLite
logbook, so the only way to a separate SQLite logbook — the whole-app "change
database location" pointer — swapped the config too, wiping the operator's setup
(reported: creating a new SQLite for a visiting op lost all profiles/settings).

Now the two are separate files:
- Settings database: settings + profiles. Fresh installs name it settings.db;
  existing installs keep opslog.db.
- Logbook (QSOs): a dedicated logbook.db next to the settings db, or a
  per-profile file (profile.ProfileDB.Path), or MySQL. connectLogbook opens the
  logbook file (db.Open creates+migrates on first use); the settings db is used
  as the logbook only if the split ever fails.

One-time, non-destructive migration at startup: if there's no logbook file yet
but the settings db already holds QSOs (legacy combined opslog.db), seed
logbook.db with a clean copy via VACUUM INTO — contacts move to the logbook, the
originals stay in the settings db as an untouched backup.

UI: the Database panel now shows the settings database and this profile's logbook
as two clearly labelled sections (+ "Open folder"), and the logbook selector is
SQLite (default logbook.db, or a dedicated file via "Choose a dedicated file…")
vs MySQL — no more confusing shared/separate choice. New binding RevealDataFolder.

frontend/wailsjs/go/models.ts

@@ -2109,6 +2109,7 @@ export namespace main {
 	    path: string;
 	    default_path: string;
 	    is_custom: boolean;
+	    logbook_default_path: string;
 	
 	    static createFrom(source: any = {}) {
 	        return new DatabaseSettings(source);
@@ -2119,6 +2120,7 @@ export namespace main {
 	        this.path = source["path"];
 	        this.default_path = source["default_path"];
 	        this.is_custom = source["is_custom"];
+	        this.logbook_default_path = source["logbook_default_path"];
 	    }
 	}
 	export class DuplicateGroup {