feat(docker): harden session mode + File Viewer button (v1.4.1)

Docker cases: seamless Claude auth (seed ~/.claude.json instead of the
corruption-prone single-file mount), full credential-store isolation for
claude + codex/gemini/gcloud/opencode (share only transcripts/rollouts,
seed the rest), auto-build the base image on first use, C.UTF-8 locale
(fixes box-drawing), collapsed/shortened Create-Case UI + short "(docker)"
case-menu tags, and w<n>-<case> tab naming for docker/remote sessions.
Also: opt-in File Viewer header button; fix a TZ-boundary flaky test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/routes/system-routes.test.ts

@@ -225,7 +225,11 @@ describe('system-routes', () => {
       harness.ctx._session.status = 'working';
       harness.ctx.store.getDailyStats.mockReturnValue([
         {
-          date: new Date().toISOString().split('T')[0],
+          // LOCAL date (not toISOString/UTC): away-digest's dayOverlapsRange parses
+          // the date as local midnight, so a UTC date near the local-midnight boundary
+          // (e.g. running at 01:xx CEST = prior-day UTC) would fall outside the 1h
+          // window and make this assertion TZ/hour-flaky.
+          date: new Date().toLocaleDateString('en-CA'),
           inputTokens: 100,
           outputTokens: 200,
           estimatedCost: 0.02,