feat(polls): let creators set max selections for multiple-choice

The poll creator only offered single (max_selections 1) or multiple = pick ALL
options — no way to run a "pick your top 2" poll, even though the display side
already enforces an arbitrary max_selections ("Select up to N"). Add a "Voters
can pick up to N of M options" control shown for multiple-choice polls. Defaults
to the option count (preserving the old select-all behavior) until lowered;
clamped to [2, filled option count] on submit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/PollCreator.tsx

@@ -34,6 +34,10 @@ export function PollCreator({ roomId, onClose }: PollCreatorProps) {
   const [question, setQuestion] = useState('');
   const [options, setOptions] = useState<string[]>(['', '']);
   const [isMultiple, setIsMultiple] = useState(false);
+  // For multiple-choice polls: the most options a voter may pick. Defaults high
+  // so an untouched multiple poll means "select all that apply" (the previous
+  // behavior); the effective value is clamped to the current option count.
+  const [maxSelections, setMaxSelections] = useState(10);
   // Results visibility: disclosed (live results, default) vs undisclosed (hidden
   // until the poll is ended).
   const [disclosed, setDisclosed] = useState(true);
@@ -85,7 +89,9 @@ export function PollCreator({ roomId, onClose }: PollCreatorProps) {
         'm.poll': {
           question: { 'm.text': trimmedQuestion },
           answers: filledOptions.map((o, i) => ({ 'm.id': `${i}`, 'm.text': o })),
-          max_selections: isMultiple ? filledOptions.length : 1,
+          max_selections: isMultiple
+            ? Math.min(Math.max(2, maxSelections), filledOptions.length)
+            : 1,
           kind: disclosed ? 'm.poll.disclosed' : 'm.poll.undisclosed',
         },
         body: fallbackBody,
@@ -222,6 +228,32 @@ export function PollCreator({ roomId, onClose }: PollCreatorProps) {
                     );
                   })}
                 </Box>
+                {isMultiple && (
+                  <Box alignItems="Center" gap="200" style={{ marginTop: config.space.S200 }}>
+                    <Text as="label" htmlFor="poll-max-select" size="T200" priority="400">
+                      Voters can pick up to
+                    </Text>
+                    <Input
+                      id="poll-max-select"
+                      variant="Background"
+                      size="300"
+                      type="number"
+                      min={2}
+                      max={options.length}
+                      value={Math.min(maxSelections, options.length)}
+                      onChange={(e: React.ChangeEvent<HTMLInputElement>) =>
+                        setMaxSelections(
+                          Math.min(options.length, Math.max(2, parseInt(e.target.value, 10) || 2)),
+                        )
+                      }
+                      style={{ width: '4rem' }}
+                      aria-label="Maximum selections per voter"
+                    />
+                    <Text size="T200" priority="300">
+                      of {options.length} options
+                    </Text>
+                  </Box>
+                )}
               </Box>
 
               {/* Results visibility */}