Bound inputs: a field that loads its value from a sibling-parameterized resource

Requirement.bind {field, param, resource}: when the watched sibling
changes (a file select, say), the bind's resource is fetched with the
sibling's value as a parameter and the result becomes this field's
value - the on-site editing flow for /develop-proposal, and a generic
select-plus-detail primitive anywhere else. Url sources gain {name}
path templating (percent-encoded, / preserved, SSRF check runs after
substitution); an empty sibling never fetches and never clears an
edit. Bound textareas render monospace.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

style/main.css

@@ -422,6 +422,16 @@ textarea {
   resize: vertical;
 }
 
+/* A bound textarea holds loaded source text - monospace, roomy, no
+   soft-wrap surprises. */
+textarea.bound {
+  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
+  font-size: 0.85rem;
+  min-height: 16rem;
+  white-space: pre;
+  overflow-x: auto;
+}
+
 input:focus,
 textarea:focus {
   outline: none;