Fix get_resource/transition_answer: scope feature lookup to its own alternative

Both resolved a feature by name flattened across every alternative on
the question, not scoped to the one the caller actually meant - fine
when every question had exactly one alternative with a resource
feature, silently wrong now that /review has three (Applicants,
Inquiries, Subscribers all use the same empty feature name). Every
lookup always resolved to the first alternative's feature - Subscribers
was reading the (empty) Applicants bucket instead of its own, and
Invite/Decline/Mark-handled buttons would have had the same problem
had two of those transitions ever been clicked side by side.

Threaded a new `alternative` parameter through get_resource,
transition_answer, and their client-side callers
(ResourceFeature/ResourceValue/AnswerRow) - the fix lives entirely in
the already-generic resource-fetching machinery, no per-alternative
special-casing.

src/answers.rs

@@ -84,6 +84,7 @@ pub async fn store_answer(
 #[server]
 pub async fn transition_answer(
     question_id: String,
+    alternative: String,
     feature_name: String,
     item_id: String,
     to: String,
@@ -100,10 +101,16 @@ pub async fn transition_answer(
         .get(&question_id)
         .cloned()
         .ok_or_else(|| ServerFnError::new("unknown question"))?;
+    // Same alternative-scoped lookup as get_resource, and for the same
+    // reason - a feature name isn't unique across a whole question,
+    // only within its own alternative.
     let feature = question
         .alternatives
         .iter()
-        .flat_map(|a| &a.features)
+        .find(|a| a.name == alternative)
+        .ok_or_else(|| ServerFnError::new("unknown alternative"))?
+        .features
+        .iter()
         .find(|f| f.name == feature_name)
         .ok_or_else(|| ServerFnError::new("unknown feature"))?;
     let resource = feature