fix(approvals,l10n,theme): usertest findings — localized prompts, no-data confirm, .chain log path, honest wording, AA contrast

- approvals: empty/legacy hub prompts render the localized fallback;
  approving without show: data asks for conscious confirmation first
- chain_log: write to ~/.chain/logs/studio-errors.log (was .fai),
  one-time best-effort migration of the legacy file + rotation sibling
- l10n: 'manipulationssicher' -> 'manipulationserkennend', neutral
  WORM-1 blurb, doctor pill 'Integritätskette v1', federation hint
  says the CA authenticates the first connect (DE+EN)
- theme: muted text token now >=4.5:1 on canvas, cards and elevated
  dark surfaces (was 3.7:1 on cards)

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/chain_log.dart

@@ -51,7 +51,31 @@ class ChainLog {
         Platform.environment['HOME'] ??
         Platform.environment['USERPROFILE'] ??
         '.';
-    return p.join(home, '.fai', 'logs', 'studio-errors.log');
+    final path = p.join(home, '.chain', 'logs', 'studio-errors.log');
+    _migrateLegacyLog(home, path);
+    return path;
+  }
+
+  // Pre-rename installs wrote to `~/.fai/logs/`. Move that file (and
+  // its rotation sibling) over once so the error trail survives the
+  // rename; never overwrite an existing new-path file. Best-effort
+  // and cheap enough to run per access (two stat calls after the
+  // first migration).
+  static void _migrateLegacyLog(String home, String newPath) {
+    try {
+      for (final suffix in const ['', '.1']) {
+        final legacy = File(
+          p.join(home, '.fai', 'logs', 'studio-errors.log$suffix'),
+        );
+        final target = File('$newPath$suffix');
+        if (legacy.existsSync() && !target.existsSync()) {
+          target.parent.createSync(recursive: true);
+          legacy.renameSync(target.path);
+        }
+      }
+    } catch (_) {
+      // Best-effort: a failed migration must not break logging.
+    }
   }
 
   /// Absolute path of the studio-errors log. Public so the