T08c: Frontend Mail UI + Global Search UI — 44 tests, tsc clean, vite build pass

- Mail page: 3-pane layout (folder tree + mail list + reading pane)
- Compose modal: rich text editor (bold/italic/link), template picker, reply/forward pre-fill
- Mail settings: accounts, signatures, rules, labels, vacation, PGP (6 tabs)
- Shared mailbox selector: switch between personal + shared accounts
- Mail search bar + attachment download + create-event-from-mail
- Global search: tabs for companies/contacts/mails/files/events
- Search autocomplete in TopBar (existing SearchDropdown)
- API client: mail.ts (all endpoints)
- Routes: /mail, /mail/settings
- i18n: de.json + en.json mail + search translations
- 44 new tests (4 test files), full regression 318/318 pass
- tsc --noEmit: 0 errors, vite build: 267 modules

.a0/next_steps.md

@@ -1,7 +1,6 @@
 # LeoCRM — Next Steps
 1. **User decision needed**: Which task next?
-   - T08a: DMS Frontend (prerequisite T04 ✅, T07b ✅ — unblocked)
-   - T08c: Mail Frontend (prerequisite T06 ✅ — now unblocked)
+   - T08c: Frontend Mail UI + Global Search UI (prerequisite T06 ✅ — unblocked)
    - T10: Monitoring, Performance, Documentation & Environment Config
 2. After task selection: delegate to implementation_engineer with briefing
 3. After implementation: test_debug_engineer for validation