fix: dedupe a repeated name in a group, and name every unmet requirement

Addresses Copilot's round-13 review on #2035. Two suppressed comments, both
real, both in the required-group work from round 7 rather than in the recent
preview rework.

1. `{a,a}` is ONE requirement named twice, but `requiredGroups` stored it as
   a two-name group, so everything downstream read it as "either of these
   will do". The TUI was left with a form it could not submit: its
   `length === 1` test marked `a` optional while ResourceTestModal's guard
   still refused a blank. The web panel offered the useless hint
   "Any one of: a, a". Names are now deduplicated within the expression --
   expansion still emits both occurrences (`x://{a,a}` -> `x://1,1`), which
   RFC 6570 requires.

2. The per-field hint used `find`, so a variable in several shared groups
   advertised only the first. With `{a,b}{b,c}{a,c}`, filling `b` satisfies
   the first two and every visible hint then looks met while Read Resource
   stays disabled on the unmet `{a,c}` -- a requirement with nothing on
   screen pointing at it.

   Fields now hint every shared group they sit in. That alone is not enough,
   because no per-field hint can say WHICH group is still outstanding, so
   the form states it directly: "Still needed: a or c", built from the same
   `unmetRequiredGroups` the submit gate uses, so the message and the button
   cannot disagree. `hasRequiredValues` is no longer called here -- the
   panel derives both from the one list.

npm run ci passes.

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/utils/uriTemplate.ts

@@ -26,6 +26,7 @@ export {
   requiredGroups,
   templateVariables,
   tryExpandUriTemplate,
+  unmetRequiredGroups,
 } from "@inspector/core/mcp/uriTemplate.js";
 export type {
   TemplateExpansion,