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/resource.rs

@@ -8,12 +8,14 @@
 
 use leptos::prelude::*;
 
-/// Fetches the live data for `question_id`'s `feature_name` feature.
-/// Fails closed: a resource with neither `public: true` nor
-/// `requires_group` set is unreachable, not "open" by omission.
+/// Fetches the live data for `question_id`'s `alternative`'s
+/// `feature_name` feature. Fails closed: a resource with neither
+/// `public: true` nor `requires_group` set is unreachable, not "open"
+/// by omission.
 #[server]
 pub async fn get_resource(
     question_id: String,
+    alternative: String,
     feature_name: String,
 ) -> Result<serde_json::Value, ServerFnError> {
     use crate::auth::{User, SESSION_USER_KEY};
@@ -26,10 +28,21 @@ pub async fn get_resource(
         .get(&question_id)
         .cloned()
         .ok_or_else(|| ServerFnError::new("unknown question"))?;
+    // Scoped to the named alternative first, not flattened across all
+    // of them - a feature name (often just "") is only unique within
+    // its own alternative, not across a whole question. Flattening
+    // silently resolved every same-named feature to whichever
+    // alternative happened to be first, so "Subscribers" (and any
+    // other later resource-listing alternative sharing an unnamed
+    // feature with an earlier one on the same question) always read
+    // the first alternative's bucket instead of its own.
     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