fix(web): allow multiline input with modifier+Enter in composer (#431)

* fix(web): allow multiline input with modifier+Enter in composer

Previously only Shift+Enter was recognized for newline insertion while
Ctrl+Enter, Alt+Enter, and Cmd+Enter all triggered message send.
This broadens the modifier check so any modifier+Enter inserts a newline.

Also sets submitOnEnter={false} to let the custom handleKeyDown manage
all Enter logic, eliminating dual-handler ambiguity with the library's
built-in submit behavior.

Closes #429

* fix(web): prevent modifier+Enter from accidentally sending messages

Only plain Enter should send; Ctrl/Alt/Cmd+Enter were incorrectly
falling through to the send path because the guard only checked
e.shiftKey. Now all non-Shift modifier combos are blocked from
sending (preventDefault + no-op).

Also keeps submitOnEnter={false} so the custom handleKeyDown is the
sole owner of Enter-key logic, avoiding dual-handler ambiguity.

Closes #429

* fix(web): restore Enter to accept autocomplete suggestions

The previous refactor made the Enter handler unconditionally return
before reaching the suggestion-selection path. Move suggestion
handling above the send/no-op block so Enter still accepts visible
autocomplete entries.

web/src/components/AssistantChat/HappyComposer.tsx

@@ -303,10 +303,18 @@ export function HappyComposer(props: {
             return // let default textarea behavior handle newline
         }
 
-        // Enter without shift: send or no-op (never insert newline)
-        if (key === 'Enter' && !e.shiftKey && suggestions.length === 0) {
+        // Enter with suggestions visible: select the suggestion
+        if (key === 'Enter' && suggestions.length > 0) {
             e.preventDefault()
-            if (canSend) {
+            const indexToSelect = selectedIndex >= 0 ? selectedIndex : 0
+            handleSuggestionSelect(indexToSelect)
+            return
+        }
+
+        // Only plain Enter (no modifiers) sends; other modifier combos are ignored
+        if (key === 'Enter') {
+            e.preventDefault()
+            if (!e.ctrlKey && !e.altKey && !e.metaKey && canSend) {
                 api.composer().send()
                 setShowContinueHint(false)
             }
@@ -324,7 +332,7 @@ export function HappyComposer(props: {
                 moveDown()
                 return
             }
-            if ((key === 'Enter' || key === 'Tab') && !e.shiftKey) {
+            if ((key === 'Tab') && !e.shiftKey) {
                 e.preventDefault()
                 const indexToSelect = selectedIndex >= 0 ? selectedIndex : 0
                 handleSuggestionSelect(indexToSelect)
@@ -768,7 +776,7 @@ export function HappyComposer(props: {
                                 placeholder={showContinueHint ? t('misc.typeMessage') : t('misc.typeAMessage')}
                                 disabled={controlsDisabled}
                                 maxRows={5}
-                                submitOnEnter={!isTouch}
+                                submitOnEnter={false}
                                 cancelOnEscape={false}
                                 onChange={handleChange}
                                 onSelect={handleSelect}