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/pages/store.dart

@@ -3252,7 +3252,7 @@ const List<TodayStoryData> _kFallbackTodayStories = <TodayStoryData>[
     badgeEn: 'AUDIT',
     badgeDe: 'AUDIT',
     titleEn: 'Tamper-evident hash chain — built in',
-    titleDe: 'Manipulationssicher per Hash-Kette — eingebaut',
+    titleDe: 'Manipulation erkennbar per Hash-Kette — eingebaut',
     bodyEn:
         'Every flow run, every install, every approval lands in ~/.chain/audit/ as a hash-chained event log. Any later edit invalidates the chain. CRA-ready out of the box — no compliance product to buy on top.',
     bodyDe: