docs: add translations and update development log (#168)

docs/development-progress-log.md

@@ -1321,6 +1321,135 @@ end
 
 ---
 
+## Session: User-Member Linking UI Enhancement (2025-01-13)
+
+### Feature Summary
+Implemented user-member linking functionality in User Edit/Create views with fuzzy search autocomplete, email conflict handling, and accessibility support.
+
+**Key Features:**
+- Autocomplete dropdown with PostgreSQL Trigram fuzzy search
+- Link/unlink members to user accounts
+- Email synchronization between linked entities
+- WCAG 2.1 AA compliant (ARIA labels)
+- Bilingual UI (English/German)
+
+### Technical Decisions
+
+**1. Search Priority Logic**
+Search query takes precedence over email filtering to provide better UX:
+- User types → fuzzy search across all unlinked members
+- Email matching only used for post-filtering when no search query present
+
+**2. JavaScript Hook for Input Value**
+Used minimal JavaScript (~6 lines) for reliable input field updates:
+```javascript
+// assets/js/app.js
+window.addEventListener("phx:set-input-value", (e) => {
+  document.getElementById(e.detail.id).value = e.detail.value
+})
+```
+**Rationale:** LiveView DOM patching has race conditions with rapid state changes in autocomplete components. Direct DOM manipulation via `push_event` is the idiomatic LiveView solution for this edge case.
+
+**3. Fuzzy Search Implementation**
+Combined PostgreSQL Full-Text Search + Trigram for optimal results:
+```sql
+-- FTS for exact word matching
+search_vector @@ websearch_to_tsquery('simple', 'greta')
+-- Trigram for typo tolerance
+word_similarity('gre', first_name) > 0.2
+-- Substring for email/IDs
+email ILIKE '%greta%'
+```
+
+### Key Learnings
+
+#### 1. Ash `manage_relationship` Internals
+**Critical Discovery:** During validation, relationship data lives in `changeset.relationships`, NOT `changeset.attributes`:
+
+```elixir
+# During validation (manage_relationship processing):
+changeset.relationships.member = [{[%{id: "uuid"}], opts}]
+changeset.attributes.member_id = nil  # Still nil!
+
+# After action completes:
+changeset.attributes.member_id = "uuid"  # Now set
+```
+
+**Solution:** Extract member_id from both sources:
+```elixir
+defp get_member_id_from_changeset(changeset) do
+  case Map.get(changeset.relationships, :member) do
+    [{[%{id: id}], _opts}] -> id           # New link
+    _ -> Ash.Changeset.get_attribute(changeset, :member_id)  # Existing
+  end
+end
+```
+
+**Impact:** Fixed email validation false positives when linking user+member with identical emails.
+
+#### 2. LiveView + JavaScript Integration Patterns
+
+**When to use JavaScript:**
+- ✅ Direct DOM manipulation (autocomplete, input values)
+- ✅ Browser APIs (clipboard, geolocation)
+- ✅ Third-party libraries
+
+**When NOT to use JavaScript:**
+- ❌ Form submissions
+- ❌ Simple show/hide logic
+- ❌ Server-side data fetching
+
+**Pattern:**
+```elixir
+socket |> push_event("event-name", %{key: value})
+```
+```javascript
+window.addEventListener("phx:event-name", (e) => { /* handle */ })
+```
+
+#### 3. PostgreSQL Trigram Search
+Requires `pg_trgm` extension with GIN indexes:
+```sql
+CREATE INDEX members_first_name_trgm_idx 
+  ON members USING GIN(first_name gin_trgm_ops);
+```
+Supports:
+- Typo tolerance: "Gret" finds "Greta"
+- Partial matching: "Mit" finds "Mitglied"  
+- Substring: "exam" finds "example.com"
+
+#### 4. Test-Driven Development for Bug Fixes
+Effective workflow:
+1. Write test that reproduces bug (should fail)
+2. Implement minimal fix
+3. Verify test passes
+4. Refactor while green
+
+**Result:** 355 tests passing, 100% backend coverage for new features.
+
+### Files Changed
+
+**Backend:**
+- `lib/membership/member.ex` - `:available_for_linking` action with fuzzy search
+- `lib/mv/accounts/user/validations/email_not_used_by_other_member.ex` - Relationship change extraction
+- `lib/mv_web/live/user_live/form.ex` - Event handlers, state management
+
+**Frontend:**
+- `assets/js/app.js` - Input value hook (6 lines)
+- `priv/gettext/**/*.po` - 10 new translation keys (DE/EN)
+
+**Tests (NEW):**
+- `test/membership/member_fuzzy_search_linking_test.exs`
+- `test/accounts/user_member_linking_email_test.exs`
+- `test/mv_web/user_live/form_member_linking_ui_test.exs`
+
+### Deployment Notes
+- **Assets:** Requires `cd assets && npm run build`
+- **Database:** No migrations (uses existing indexes)
+- **Config:** No changes required
+
+---
+
 ## Conclusion
 
 This project demonstrates a modern Phoenix application built with: