feat(threads): add editing, moderation retry, and emoji reactions

Add API routes and UI for editing threads and messages
Allow users to retry AI moderation for failed messages
Migrate thread reactions to use native emojis
Implement frontend search filtering for thread list

frontend/src/styles/main.css

@@ -100,6 +100,18 @@ svg {
   flex: 0 0 auto;
 }
 
+.sr-only {
+  position: absolute !important;
+  width: 1px !important;
+  height: 1px !important;
+  padding: 0 !important;
+  margin: -1px !important;
+  overflow: hidden !important;
+  clip: rect(0, 0, 0, 0) !important;
+  white-space: nowrap !important;
+  border: 0 !important;
+}
+
 :focus-visible {
   outline: 3px solid var(--focus);
   outline-offset: 3px;
@@ -9692,7 +9704,7 @@ button:disabled,
 .threads-layout {
   min-height: min(78vh, 860px);
   display: grid;
-  grid-template-columns: minmax(180px, 220px) minmax(260px, 360px) minmax(0, 1fr);
+  grid-template-columns: minmax(180px, 220px) minmax(0, 1fr);
   gap: 16px;
   align-items: stretch;
 }
@@ -9762,12 +9774,52 @@ button:disabled,
 
 .threads-list-panel {
   display: grid;
-  grid-template-rows: auto auto minmax(0, 1fr);
+  grid-template-rows: auto auto auto minmax(0, 1fr);
   gap: 12px;
   padding: 14px;
   overflow: hidden;
 }
 
+.thread-search-create {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) auto;
+  gap: 10px;
+  align-items: end;
+}
+
+.thread-search-control {
+  min-width: 0;
+  min-height: 44px;
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 0 12px;
+  border: 1px solid var(--line);
+  border-radius: var(--radius-control);
+  background: var(--surface-soft);
+  color: var(--muted);
+}
+
+.thread-search-control .ui-icon {
+  width: 20px;
+  height: 20px;
+  flex: 0 0 auto;
+}
+
+.thread-search-control input {
+  width: 100%;
+  min-width: 0;
+  border: 0;
+  background: transparent;
+  color: var(--ink);
+  outline: 0;
+}
+
+.thread-search-control:focus-within {
+  border-color: var(--focus);
+  box-shadow: 0 0 0 3px color-mix(in srgb, var(--focus) 16%, transparent);
+}
+
 .thread-filters {
   display: grid;
   grid-template-columns: repeat(2, minmax(0, 1fr));
@@ -9782,7 +9834,6 @@ button:disabled,
   font-weight: 900;
 }
 
-.thread-filters select,
 .thread-composer textarea {
   width: 100%;
 }
@@ -9864,9 +9915,16 @@ button.thread-chip {
   overflow: hidden;
 }
 
+.thread-chat-panel--modal {
+  min-height: min(72vh, 680px);
+  border: 0;
+  border-radius: 0;
+  box-shadow: none;
+}
+
 .thread-chat-header {
   display: flex;
-  justify-content: space-between;
+  justify-content: flex-end;
   gap: 14px;
   padding: 16px;
   border-bottom: 1px solid var(--line);
@@ -9894,6 +9952,7 @@ button.thread-chip {
   display: flex;
   flex-wrap: wrap;
   gap: 6px;
+  align-items: center;
   padding: 10px 16px;
   border-bottom: 1px solid var(--line);
 }
@@ -9923,6 +9982,17 @@ button.thread-chip {
   color: var(--ink);
 }
 
+.thread-reaction__emoji {
+  font-size: 17px;
+  line-height: 1;
+}
+
+.thread-reaction--action {
+  padding: 4px 9px;
+  font-size: 13px;
+  font-weight: 900;
+}
+
 .thread-message-scroll {
   min-height: 0;
   overflow: auto;
@@ -9976,6 +10046,24 @@ button.thread-chip {
   white-space: pre-wrap;
 }
 
+.thread-message-edit {
+  display: grid;
+  gap: 8px;
+}
+
+.thread-message-edit textarea {
+  width: 100%;
+  min-height: 92px;
+  resize: vertical;
+}
+
+.thread-message-actions {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+  align-items: center;
+}
+
 .thread-composer {
   display: grid;
   grid-template-columns: minmax(0, 1fr) auto;
@@ -10018,10 +10106,6 @@ button.thread-chip {
   .threads-layout {
     grid-template-columns: minmax(180px, 220px) minmax(0, 1fr);
   }
-
-  .thread-chat-panel {
-    grid-column: 1 / -1;
-  }
 }
 
 @media (max-width: 640px) {
@@ -10031,6 +10115,7 @@ button.thread-chip {
     grid-template-columns: 1fr;
   }
 
+  .thread-search-create,
   .thread-filters,
   .thread-composer,
   .thread-chat-header {