Chat tabs, chat mode, own modes, compaction notice, CLI binaries again

- Terminals and file managers as tabs of a chat; chat terminals keep running on
  the server (no idle timeout) and re-attach from any device
- "Just chat" in New session and a built-in chat mode with a lean prompt and only
  web tools; custom modes with kind (coding/conversation), read-only and tool picker
- Mode selector as a dropdown
- The chat shows running compactions (automatic: tokens and share of the limit)
  and labels summaries
- Docker image builds and serves the terminal client binaries again
- Fix: atomic session updates; background title/usage writes no longer undo each
  other (auto compaction triggered one turn late)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/styles.css

@@ -3603,3 +3603,125 @@ button.danger-solid {
 .plan-pct {
   font-variant-numeric: tabular-nums;
 }
+
+/* --- chat tabs (chat + terminals) ---------------------------------------------- */
+.chat-tabs {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  padding: 4px 10px 0;
+  border-bottom: 1px solid var(--bg3);
+  overflow-x: auto;
+  flex: none;
+}
+.chat-tab {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  padding: 6px 12px;
+  border: none;
+  border-bottom: 2px solid transparent;
+  border-radius: 6px 6px 0 0;
+  background: none;
+  color: var(--fg2);
+  font-size: 13px;
+  white-space: nowrap;
+  cursor: pointer;
+}
+span.chat-tab {
+  padding: 0 4px 0 0;
+}
+span.chat-tab > button {
+  padding: 6px 4px 6px 12px;
+  color: inherit;
+  font-size: 13px;
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+}
+.chat-tab .close {
+  padding: 2px 4px;
+  opacity: 0.6;
+}
+.chat-tab .close:hover {
+  opacity: 1;
+}
+.chat-tab:hover {
+  background: var(--bg1);
+  color: var(--fg0);
+}
+.chat-tab.active {
+  color: var(--fg0);
+  border-bottom-color: var(--accent);
+  background: var(--bg1);
+}
+.chat-tab.dead {
+  opacity: 0.55;
+}
+.chat-tab-add {
+  padding: 4px 8px;
+}
+.chat-pane {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+}
+.chat-pane[hidden] {
+  display: none;
+}
+.files-embed-bar {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 6px 12px;
+  border-bottom: 1px solid var(--bg3);
+  flex: none;
+}
+.files-embed-bar .path {
+  font-size: 12px;
+  color: var(--fg3);
+  font-family: var(--mono);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.tool-picker .hint {
+  margin-bottom: 6px;
+}
+.tool-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(170px, 1fr));
+  gap: 4px 12px;
+}
+.tool-item {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 12px;
+  cursor: pointer;
+}
+.tool-item.disabled {
+  opacity: 0.45;
+  cursor: default;
+}
+.mode-select {
+  font-weight: 600;
+  color: var(--accent);
+}
+
+.compacting-card {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  margin: 10px 0;
+  padding: 10px 14px;
+  border: 1px dashed var(--bg3);
+  border-radius: var(--radius);
+  background: var(--bg1);
+  font-size: 13px;
+}
+.compacting-card.auto {
+  border-color: color-mix(in srgb, var(--accent) 60%, var(--bg3));
+}