feat(studio): plain-language store, bottom-anchored ask bar (v0.33.0)

The store had three structural problems flagged in user
feedback:

1. "Lernkurve zu hoch — alle bridge, debug, alpha, planned,
   keiner weiß was das heißt." Wire-level enum values bled
   through into the UI: `bridge`, `debug`, `published`,
   `alpha`, `planned`. Operators don't share the data model.

2. "Filter / Kategorien sollten oben in die Leiste neben Store
   zum ausklappen, der Body soll übersichtlicher werden." A
   chip-row plus category strip plus result-count line ate a
   full row of viewport on every screen.

3. "Suche passt besser an den unteren Bildschirmrand." The
   chat-style ask bar belongs at the bottom — Claude / ChatGPT
   / Slack pattern — not at the top where it competes with
   the Today hero.

Plus: "Es gibt noch ganz viele overflows in den Beschreibungen."

Changes:

- Plain-language display names. New ARB keys for category
  labels (Connectors / Sample modules / AI models / Storage /
  Channels / Authentication / Orchestration / …) and updated
  status values (stable / experimental / coming soon). Wire
  ids stay in StoreEntry, RPCs, seed.yaml — only the rendered
  pills and dropdowns get translated. Helpers
  `_categoryDisplayName` and `_statusDisplayName` keep the
  mapping in one place.

- Toolbar moves into the AppBar. The new `_CategoryDropdown`
  hosts the category picker as a popup-menu with localised
  labels; the existing `_FilterButton` lives next to it; the
  reload icon stays where it always was. The body no longer
  carries any chip strip or result-count line.

- Bottom-anchored `_AskBar`. The Scaffold body becomes a
  Column of `Expanded(scrollable content)` plus a pinned
  composer row at the foot of the viewport, with a top
  divider matching the chat-input pattern of modern AI
  assistants. AI answers now render at the top of the scroll
  (above the Today-Hero) so the operator sees them right
  after submitting the question at the bottom.

- Overflow sweep on descriptions. Today-Hero header row
  becomes a Wrap (badge + deck flow naturally on narrow
  windows), the title is bound to 3 lines, the body to 6.
  Card category text gets `maxLines: 1, ellipsis` in both
  StoreCard and FeaturedTile. Recommended-source card title
  gets the same treatment.

- Better toast for the "added but zero capabilities" path.
  When MCP discovery succeeds but returns no tools (typical
  Streamable-HTTP servers without Mcp-Session-Id support, or
  servers that need `notifications/initialized`), the toast
  now explains the situation in plain language and points
  the operator at Settings → MCP Clients to retry. Old
  pluralised toast still fires when N > 0.

Hub-side `notifications/initialized` for HTTP MCP and
Mcp-Session-Id support are out of scope for this commit;
tracked as a separate fai_hub follow-up.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_localizations.dart

@@ -761,19 +761,19 @@ abstract class AppLocalizations {
   /// No description provided for @storeStatusPublished.
   ///
   /// In en, this message translates to:
-  /// **'Published'**
+  /// **'stable'**
   String get storeStatusPublished;
 
   /// No description provided for @storeStatusAlpha.
   ///
   /// In en, this message translates to:
-  /// **'Alpha'**
+  /// **'experimental'**
   String get storeStatusAlpha;
 
   /// No description provided for @storeStatusPlanned.
   ///
   /// In en, this message translates to:
-  /// **'Planned'**
+  /// **'coming soon'**
   String get storeStatusPlanned;
 
   /// No description provided for @storeInstalledOnly.
@@ -782,6 +782,78 @@ abstract class AppLocalizations {
   /// **'Installed'**
   String get storeInstalledOnly;
 
+  /// No description provided for @storeCategoryLabel.
+  ///
+  /// In en, this message translates to:
+  /// **'Category'**
+  String get storeCategoryLabel;
+
+  /// No description provided for @storeCategoryAll.
+  ///
+  /// In en, this message translates to:
+  /// **'All categories'**
+  String get storeCategoryAll;
+
+  /// No description provided for @storeCategoryBridge.
+  ///
+  /// In en, this message translates to:
+  /// **'Connectors'**
+  String get storeCategoryBridge;
+
+  /// No description provided for @storeCategoryDebug.
+  ///
+  /// In en, this message translates to:
+  /// **'Sample modules'**
+  String get storeCategoryDebug;
+
+  /// No description provided for @storeCategoryText.
+  ///
+  /// In en, this message translates to:
+  /// **'Text'**
+  String get storeCategoryText;
+
+  /// No description provided for @storeCategoryLlm.
+  ///
+  /// In en, this message translates to:
+  /// **'AI models'**
+  String get storeCategoryLlm;
+
+  /// No description provided for @storeCategorySystem.
+  ///
+  /// In en, this message translates to:
+  /// **'System'**
+  String get storeCategorySystem;
+
+  /// No description provided for @storeCategoryAuth.
+  ///
+  /// In en, this message translates to:
+  /// **'Authentication'**
+  String get storeCategoryAuth;
+
+  /// No description provided for @storeCategoryStorage.
+  ///
+  /// In en, this message translates to:
+  /// **'Storage'**
+  String get storeCategoryStorage;
+
+  /// No description provided for @storeCategoryChannel.
+  ///
+  /// In en, this message translates to:
+  /// **'Channels'**
+  String get storeCategoryChannel;
+
+  /// No description provided for @storeCategoryWeb.
+  ///
+  /// In en, this message translates to:
+  /// **'Web'**
+  String get storeCategoryWeb;
+
+  /// No description provided for @storeCategoryOrchestrator.
+  ///
+  /// In en, this message translates to:
+  /// **'Orchestration'**
+  String get storeCategoryOrchestrator;
+
   /// No description provided for @storeNResults.
   ///
   /// In en, this message translates to:
@@ -1100,6 +1172,12 @@ abstract class AppLocalizations {
   /// **'Added {name} — {n} federated {n, plural, =1{capability} other{capabilities}}.'**
   String storeProviderAddedToast(String name, int n);
 
+  /// No description provided for @storeProviderAddedZeroToast.
+  ///
+  /// In en, this message translates to:
+  /// **'{name} registered, but the server returned no capabilities yet. Open Settings → MCP Clients to retry discovery or check the server.'**
+  String storeProviderAddedZeroToast(String name);
+
   /// No description provided for @storeProviderAddFailed.
   ///
   /// In en, this message translates to: