Improve member view table behavior+style, fix config settings (#493)

## Description of the implemented changes
The changes were:
- [x] Bugfixing
- [x] New Feature
- [ ] Breaking Change
- [x] Refactoring

This PR standardizes interactive table behavior and improves settings robustness.
It makes the new hover/focus-visible row highlight the default for clickable tables, keeps sticky first-column behavior configurable (and optimized for member selection UX), and tightens SMTP source-of-truth handling so ENV-based and UI-based configuration do not conflict.

## What has been changed?
- Refactored `CoreComponents.table` to expose interaction state via `data-row-interactive` and moved default row hover/focus styling to CSS.
- Made the new row highlight behavior (`hover` + `:has(:focus-visible)`) the default for clickable zebra tables.
- Kept sticky-first-column as an explicit table option and preserved sticky-specific selection accent behavior.
- Updated member overview table usage to the sticky-first-column mode and refined scrolling behavior (table scrollbar within container, not page-coupled).
- Adjusted table-related tests to validate the new interaction contract (attribute/CSS-driven behavior instead of legacy ring classes).
- Improved SMTP config handling:
  - clearer ENV-vs-Settings behavior (ENV-only mode when host env is set),
  - read-only and warning behavior in global settings UI when required env keys are missing,
  - updated related config/tests/docs.
- Updated docs and changelog (`CHANGELOG.md`, `DESIGN_GUIDELINES.md`, `CODE_GUIDELINES.md`, SMTP concept docs).
- Updated gettext catalogs (`default.pot`, `en`, `de`) for new/changed UI strings.

## Definition of Done
### Code Quality
- [x] No new technical depths
- [x] Linting passed
- [x] Documentation is added were needed

### Accessibility
- [x] New elements are properly defined with html-tags
- [x] Colour contrast follows WCAG criteria
- [x] Aria labels are added when needed
- [x] Everything is accessible by keyboard
- [x] Tab-Order is comprehensible
- [x] All interactive elements have a visible focus

### Testing
- [x] Tests for new code are written
- [x] All tests pass
- [ ] axe-core dev tools show no critical or major issues

## Additional Notes
- Branch includes 4 commits:
  - `fix: make sure smtp can be set either via env or ui`
  - `fix: make horizontal scrollbars sticky to bottom`
  - `docs: update changelog`
  - `feat: make checkbox column in member view sticky`
- Full fast suite passed (`mix test --exclude slow --exclude ui`): 2017 tests, 0 failures (plus expected non-failing warning logs in test output).
- Reviewer focus areas:
  1. **Cross-table UX consistency** after moving row interaction styling to component/CSS contract.
  2. **Sticky table behavior** (selection accent stripe, zebra background, keyboard focus visibility).
  3. **SMTP precedence and UI constraints** in global settings when ENV mode is active.
  4. **Regression risk in tests** that previously asserted ring-based row classes.
- No breaking API changes expected; behavior change is primarily visual/interaction-level and intentional.

Reviewed-on: #493
Co-authored-by: Simon <s.thiessen@local-it.org>
Co-committed-by: Simon <s.thiessen@local-it.org>

test/mv/config_smtp_test.exs

@@ -2,7 +2,7 @@ defmodule Mv.ConfigSmtpTest do
   @moduledoc """
   Unit tests for Mv.Config SMTP-related helpers.
 
-  ENV overrides Settings (same pattern as OIDC/Vereinfacht). Uses real ENV and
+  SMTP uses ENV-only mode when SMTP_HOST is set. Uses real ENV and
   Settings; no mocking so we test the actual precedence. async: false because
   we mutate ENV.
   """
@@ -23,7 +23,8 @@ defmodule Mv.ConfigSmtpTest do
   end
 
   describe "smtp_port/0" do
-    test "returns parsed integer when SMTP_PORT ENV is set" do
+    test "returns parsed integer when SMTP_PORT ENV is set in ENV-only mode" do
+      set_smtp_env("SMTP_HOST", "smtp.example.com")
       set_smtp_env("SMTP_PORT", "587")
       assert Mv.Config.smtp_port() == 587
     after
@@ -51,30 +52,40 @@ defmodule Mv.ConfigSmtpTest do
     end
   end
 
-  describe "smtp_env_configured?/0" do
-    test "returns true when any SMTP ENV variable is set" do
+  describe "smtp_env_mode?/0" do
+    test "returns true when SMTP_HOST is set" do
       set_smtp_env("SMTP_HOST", "smtp.example.com")
-      assert Mv.Config.smtp_env_configured?() == true
+      assert Mv.Config.smtp_env_mode?() == true
+    after
+      clear_smtp_env()
+    end
+
+    test "returns false when SMTP_HOST is not set even if other SMTP ENV variables are set" do
+      set_smtp_env("SMTP_USERNAME", "user@example.com")
+      set_smtp_env("SMTP_PASSWORD", "secret")
+      refute Mv.Config.smtp_env_mode?()
     after
       clear_smtp_env()
     end
 
     test "returns false when no SMTP ENV variables are set" do
       clear_smtp_env()
-      refute Mv.Config.smtp_env_configured?()
+      refute Mv.Config.smtp_env_mode?()
     end
   end
 
   describe "smtp_password/0 and SMTP_PASSWORD_FILE" do
-    test "returns value from SMTP_PASSWORD when set" do
+    test "returns value from SMTP_PASSWORD when set in ENV-only mode" do
+      set_smtp_env("SMTP_HOST", "smtp.example.com")
       set_smtp_env("SMTP_PASSWORD", "env-secret")
       assert Mv.Config.smtp_password() == "env-secret"
     after
       clear_smtp_env()
     end
 
-    test "returns content of file when SMTP_PASSWORD_FILE is set and SMTP_PASSWORD is not" do
+    test "returns content of file when SMTP_PASSWORD_FILE is set in ENV-only mode and SMTP_PASSWORD is not" do
       clear_smtp_env()
+      set_smtp_env("SMTP_HOST", "smtp.example.com")
       path = Path.join(System.tmp_dir!(), "mv_smtp_test_#{System.unique_integer([:positive])}")
       File.write!(path, "file-secret\n")
       Process.put(:smtp_password_file_path, path)
@@ -85,7 +96,8 @@ defmodule Mv.ConfigSmtpTest do
       if path = Process.get(:smtp_password_file_path), do: File.rm(path)
     end
 
-    test "SMTP_PASSWORD overrides SMTP_PASSWORD_FILE when both are set" do
+    test "SMTP_PASSWORD overrides SMTP_PASSWORD_FILE in ENV-only mode when both are set" do
+      set_smtp_env("SMTP_HOST", "smtp.example.com")
       path = Path.join(System.tmp_dir!(), "mv_smtp_test_#{System.unique_integer([:positive])}")
       File.write!(path, "file-secret")
       Process.put(:smtp_password_file_path, path)