docs(260329-u4z): complete deutsche-umlaute plan

- Added SUMMARY.md for quick task 260329-u4z
- Updated STATE.md with task completion and session info

.planning/STATE.md

@@ -5,7 +5,7 @@ milestone_name: milestone
 status: verifying
 stopped_at: Completed 04-04-PLAN.md
 last_updated: "2026-03-29T19:26:12Z"
-last_activity: 2026-03-29 - Completed quick task 260329-u1d: Kindgerechte Erklaerung auf Waldscreen hinzugefuegt
+last_activity: 2026-03-29 - Completed quick task 260329-u4z: Deutsche Umlaute in UI-Texten und CLAUDE.md
 progress:
   total_phases: 4
   completed_phases: 4
@@ -129,9 +129,10 @@ None yet.
 | 260329-ton | Markdown in Companion-Texten zu HTML rendern | 2026-03-29 | d038cc3 | [260329-ton-markdown-in-companion-texten-zu-html-ren](./quick/260329-ton-markdown-in-companion-texten-zu-html-ren/) |
 | 260329-tv5 | Uebungsanleitung dauerhaft statt Titel anzeigen | 2026-03-29 | bbb1edb | [260329-tv5-bungsanleitung-dauerhaft-statt-titel-anz](./quick/260329-tv5-bungsanleitung-dauerhaft-statt-titel-anz/) |
 | 260329-u1d | Kindgerechte Erklaerung auf Waldscreen hinzugefuegt | 2026-03-29 | cf21710 | [260329-u1d-kindgerechte-erkl-rung-auf-waldscreen-hi](./quick/260329-u1d-kindgerechte-erkl-rung-auf-waldscreen-hi/) |
+| 260329-u4z | Deutsche Umlaute in UI-Texten und CLAUDE.md | 2026-03-29 | 2691d99 | [260329-u4z-deutsche-umlaute-in-ui-texten-und-claude](./quick/260329-u4z-deutsche-umlaute-in-ui-texten-und-claude/) |
 
 ## Session Continuity
 
-Last session: 2026-03-29T19:40:00Z
+Last session: 2026-03-29T19:50:00Z
-Stopped at: Completed quick task 260329-u1d
+Stopped at: Completed quick task 260329-u4z
 Resume file: None

.planning/quick/260329-u4z-deutsche-umlaute-in-ui-texten-und-claude/260329-u4z-SUMMARY.md

@@ -0,0 +1,65 @@
+---
+phase: quick
+plan: 260329-u4z
+subsystem: ui
+tags: [i18n, german, umlauts, content]
+key-files:
+  modified:
+    - index.html
+    - src/ui/screens.ts
+    - src/companion/fallbacks.ts
+    - src/app.ts
+    - CLAUDE.md
+decisions:
+  - "UI strings must use proper German umlauts (ä, ö, ü, ß) — never ae/oe/ue transliterations"
+metrics:
+  duration: 4min
+  completed: 2026-03-29
+  tasks: 2
+  files: 5
+---
+
+# Quick Task 260329-u4z: Deutsche Umlaute in UI-Texten und CLAUDE.md Summary
+
+**One-liner:** Replaced all ae/oe/ue ASCII transliterations with proper German umlauts in all user-visible UI strings across 4 source files, and documented the convention in CLAUDE.md.
+
+## Tasks Completed
+
+| Task | Name | Commit | Files |
+|------|------|--------|-------|
+| 1 | Replace ae/oe/ue transliterations with proper umlauts | 10849b3 | index.html, src/ui/screens.ts, src/companion/fallbacks.ts, src/app.ts |
+| 2 | Document umlaut convention in CLAUDE.md | 2691d99 | CLAUDE.md |
+
+## What Was Done
+
+**Task 1 — Umlaut replacements in UI strings:**
+
+- `index.html`: Fixed forest intro paragraph (Waehle→Wähle, uebe→übe, Uebung→Übung, waechst→wächst, Naechstes→Nächstes) and parent section headings (Uebungstage→Übungstage, Haeufigste→Häufigste)
+- `src/ui/screens.ts`: Fixed 2 encouragement messages (Naechstes→Nächstes, schoener→schöner) and 2 phase labels (ueben→üben, Druecke→Drücke, herunterfaellt→herunterfällt, Woerter→Wörter, grosse→große, drueckst→drückst)
+- `src/companion/fallbacks.ts`: Fixed 7 greeting/comment strings spanning morning greetings (Frueh→Früh, schoensten→schönsten, Schoen→Schön, Gluehwuermchen→Glühwürmchen), forest comments (waechst→wächst, naechstes→nächstes, Baeumen→Bäumen, Stueck→Stück, schoen→schön, veraendert→verändert), and letter intro texts (Spuerst→Spürst, Huegel→Hügel, grosse→große, drueckst/druecken→drückst/drücken, Oe→Ö)
+- `src/app.ts`: Fixed 2 code comments (ueben→üben, Zurueck→Zurück)
+
+**Task 2 — CLAUDE.md convention:**
+
+Added to the Conventions section:
+> Immer deutsche Umlaute (ä, ö, ü, Ä, Ö, Ü, ß) in UI-Texten verwenden, niemals ae/oe/ue Transliterierung.
+
+## Verification
+
+- Grep for all transliteration patterns returned zero matches (exit code 1)
+- `npx vite build` completed successfully in 556ms with no errors
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Known Stubs
+
+None.
+
+## Self-Check: PASSED
+
+- All 5 files modified as specified
+- Commits 10849b3 and 2691d99 exist in git history
+- Build passes
+- Zero transliterations remain in scanned files