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_en.arb

@@ -128,10 +128,22 @@
   "storeNoMatchesHint": "Adjust the filters or clear the search to see all entries.",
   "storeClearFilters": "Clear filters",
   "storeStatusAll": "All",
-  "storeStatusPublished": "Published",
-  "storeStatusAlpha": "Alpha",
-  "storeStatusPlanned": "Planned",
+  "storeStatusPublished": "stable",
+  "storeStatusAlpha": "experimental",
+  "storeStatusPlanned": "coming soon",
   "storeInstalledOnly": "Installed",
+  "storeCategoryLabel": "Category",
+  "storeCategoryAll": "All categories",
+  "storeCategoryBridge": "Connectors",
+  "storeCategoryDebug": "Sample modules",
+  "storeCategoryText": "Text",
+  "storeCategoryLlm": "AI models",
+  "storeCategorySystem": "System",
+  "storeCategoryAuth": "Authentication",
+  "storeCategoryStorage": "Storage",
+  "storeCategoryChannel": "Channels",
+  "storeCategoryWeb": "Web",
+  "storeCategoryOrchestrator": "Orchestration",
   "storeNResults": "{n} result{n, plural, =1{} other{s}}",
   "@storeNResults": {
     "placeholders": { "n": { "type": "int" } }
@@ -222,6 +234,10 @@
       "n": { "type": "int" }
     }
   },
+  "storeProviderAddedZeroToast": "{name} registered, but the server returned no capabilities yet. Open Settings → MCP Clients to retry discovery or check the server.",
+  "@storeProviderAddedZeroToast": {
+    "placeholders": { "name": { "type": "String" } }
+  },
   "storeProviderAddFailed": "Could not add {name}: {error}",
   "@storeProviderAddFailed": {
     "placeholders": {