Let the coordinator create bots and put them in workspaces

The coordinator had no tool to add a worker, so a request to create one
fell back to update_workspace and wrote a bot that did not exist into the
workspace context. create_bot now adds a worker with its name, role and
instructions and joins it to a workspace, and add_bot_to_workspace puts an
existing worker in one. Both are coordinator-only and chat-replies-only,
and createBot still enforces the crew-manager check.

The coordinator's prompts now say how a bot gets created, and that one
which does not exist is never written into workspace context.

pick-free-hue moves to utils so the tool can pick a hue without importing
from layouts.

src/utils/pick-free-hue.ts

@@ -0,0 +1,22 @@
+import { BotHues, type BotHue } from "@/src/dict/bot-dict";
+
+type Params = {
+    /**
+     * Hues the crew already has.
+     */
+    taken: (string | null | undefined)[];
+};
+
+/**
+ * The first hue nobody on the crew has yet, else the least used one, so a
+ * new bot is told apart at a glance.
+ */
+export default function pickFreeHue({ taken }: Params): BotHue {
+    const counts = new Map<string, number>(BotHues.map((hue) => [hue.value, 0]));
+
+    for (const hue of taken) {
+        if (hue && counts.has(hue)) counts.set(hue, counts.get(hue)! + 1);
+    }
+
+    return [...BotHues].sort((a, b) => counts.get(a.value)! - counts.get(b.value)!)[0]!.value;
+}