Nests: team rooms with core crows and borrowing

- Server: nests API, persistence, core-first picking, borrowed flag
  (built by the backend agent against EVENTS.md; tests pass with -race)
- UI: nests in the sidebar, one feed per nest, header shows the core
  team, New nest dialog, borrowed crows labeled, per-nest waiting count
- start.command: one-click local server in controlled mode (mock crows,
  localhost only, state in .crows/)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UQnSw4RRWp8uqpj3nsnnXF

ui/src/style.css

@@ -73,6 +73,47 @@ body { margin: 0; background: var(--paper); color: var(--ink); font: 500 17px/1.
 }
 .who input:focus { outline: none; border-bottom-width: 3px; }
 
+/* ---------- nests: rooms, like channels ---------- */
+.nests { display: flex; flex-direction: column; gap: 2px; }
+.nest-link {
+  display: flex; align-items: center; justify-content: space-between; gap: 8px; width: 100%;
+  padding: 8px 10px; border: 0; border-radius: var(--corner); background: none; cursor: pointer;
+  font: 400 17px/1.2 var(--display); color: var(--muted); text-align: left;
+}
+.nest-link[aria-current="true"] { color: var(--ink); background: rgb(28 25 21 / 0.06); }
+.nest-link:focus-visible { outline: none; text-decoration: underline 2px; text-underline-offset: 4px; }
+.nest-count:not(:empty) {
+  padding: 0 7px; border-radius: 999px; background: var(--red); color: var(--paper); font: 700 12px/1.4 var(--body);
+}
+.new-nest {
+  align-self: flex-start; margin: 2px 4px 6px; padding: 4px 6px; border: 0; background: none; cursor: pointer;
+  font: italic 500 15px/1.2 var(--body); color: var(--muted);
+}
+.new-nest:hover { color: var(--ink); }
+.new-nest:focus-visible { outline: none; text-decoration: underline 2px; text-underline-offset: 4px; }
+
+/* ---------- new nest dialog: a card on the page, no outline ---------- */
+.nest-dialog { width: min(440px, calc(100vw - 32px)); padding: 0; color: var(--ink); overflow: visible; }
+.nest-dialog::backdrop { background: rgb(28 25 21 / 0.25); }
+.nest-dialog form { padding: 22px 22px 18px; }
+.nest-dialog h2 { margin: 0; font: 400 24px/1.1 var(--display); }
+.dialog-sub { margin: 6px 0 16px; color: var(--muted); font-style: italic; font-size: 15px; }
+.dialog-field { display: block; color: var(--muted); font-style: italic; font-size: 15px; }
+.dialog-field input {
+  display: block; width: 100%; margin-top: 4px; padding: 2px 0; font: 500 18px var(--body); color: var(--ink);
+  background: transparent; border: 0; border-bottom: 2px solid var(--ink);
+}
+.dialog-field input:focus { outline: none; border-bottom-width: 3px; }
+.pick { margin: 18px 0 0; padding: 0; border: 0; }
+.pick legend { padding: 0; color: var(--muted); font-style: italic; font-size: 15px; }
+.pick-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 4px; margin-top: 8px; }
+.pick-crow { display: flex; align-items: center; gap: 10px; padding: 6px 8px; border-radius: var(--corner); cursor: pointer; font: 400 16px var(--display); }
+.pick-crow:has(input:checked) { background: rgb(28 25 21 / 0.07); }
+.pick-crow input { accent-color: var(--ink); width: 16px; height: 16px; margin: 0; }
+.pick-crow .avatar { width: 30px; height: 28px; margin: 0; }
+.dialog-actions { display: flex; justify-content: flex-end; gap: 12px; margin-top: 18px; }
+.nest-dialog .err { margin: 10px 0 0; }
+
 /* ---------- roster: one list tile per crow, newest update on top ---------- */
 .roster { display: flex; flex-direction: column; gap: 6px; }
 .tile {
@@ -146,7 +187,9 @@ body { margin: 0; background: var(--paper); color: var(--ink); font: 500 17px/1.
   -webkit-mask-image: linear-gradient(rgb(0 0 0 / 0.55), transparent); mask-image: linear-gradient(rgb(0 0 0 / 0.55), transparent);
 }
 
+.feeds { display: grid; min-height: 0; }
 .feed { list-style: none; margin: 0; padding: 20px 0 10px; overflow-y: auto; min-height: 0; }
+.feed[hidden] { display: none; }
 .msg { display: grid; grid-template-columns: 40px 1fr; gap: 0 14px; padding: 14px 28px; }
 @media (hover: hover) { .msg:hover { background: rgb(28 25 21 / 0.03); } }
 /* Consecutive messages from one author group under a single name, Slack style. */