refactor(ai-create): clarify prompt-rule naming and label the counter

- Rename AiPromptRules::promptRule() to wizardPromptRule() so the asymmetry is
  explicit: only the create wizard carries a minimum; the editor's generation
  reuses just the shared maximum.
- Add aria-live and a data-testid to the prompt counter so the over-limit state
  is announced to assistive tech and reachable from browser tests.

app/Http/Requests/App/Ai/StartPostCreationRequest.php

@@ -34,7 +34,7 @@ public function rules(): array
             ],
             'social_account_id' => ['nullable', 'uuid'],
             'image_count' => ['nullable', 'integer', 'min:0', 'max:10'],
-            'prompt' => AiPromptRules::promptRule(),
+            'prompt' => AiPromptRules::wizardPromptRule(),
             'date' => ['nullable', 'date_format:Y-m-d'],
             'template' => ['sometimes', 'string', Rule::enum(ContentStyle::class)],
         ];

app/Support/AiPromptRules.php

@@ -23,11 +23,13 @@ class AiPromptRules
     public const PROMPT_MAX_LENGTH = 2000;
 
     /**
-     * Validation rules for the create wizard's generation prompt.
+     * Validation rules for the create wizard's generation prompt. The editor's
+     * content generation reuses only PROMPT_MAX_LENGTH — it has no minimum,
+     * since it has no character counter to mirror one.
      *
      * @return array<int, string>
      */
-    public static function promptRule(): array
+    public static function wizardPromptRule(): array
     {
         return ['required', 'string', 'min:'.self::PROMPT_MIN_LENGTH, 'max:'.self::PROMPT_MAX_LENGTH];
     }

resources/js/components/posts/create/AiPostWizard.vue

@@ -364,6 +364,8 @@ const startGeneration = async () => {
                 class="min-h-[140px] resize-none"
             />
             <p
+                data-testid="ai-prompt-counter"
+                aria-live="polite"
                 class="text-right text-xs tabular-nums"
                 :class="promptLength > PROMPT_MAX ? 'font-semibold text-destructive' : 'text-muted-foreground'"
             >