Add web chat tab, 24h archive policy, and clear-chat

Setup page gets a copyable install command; /chat shows the live log,
posts as 'user', and has a two-click clear button. Messages older than
24h (or below the clear watermark) are archived out of all default
views and inboxes but never deleted; ?archived=1 retrieves them.

test/api.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, test } from "bun:test";
 
 process.env.AGENTCHAT_DB = ":memory:";
 const { handle } = await import("../src/server");
+const { db } = await import("../src/db");
 
 async function post(path: string, body: unknown): Promise<Response> {
   return handle(
@@ -74,6 +75,48 @@ describe("agents", () => {
   });
 });
 
+describe("archive and clear", () => {
+  test("messages older than 24h disappear from active views but stay in the archive", async () => {
+    const old = (await (await post("/api/messages", { from: "a", to: "b", body: "stale" })).json()) as Message;
+    db.query(`UPDATE messages SET ts = strftime('%Y-%m-%dT%H:%M:%SZ', 'now', '-25 hours') WHERE id = $id`).run({
+      $id: old.id,
+    });
+
+    const active = await getJson<Message[]>("/api/messages?for=b");
+    expect(active.map((m) => m.body)).not.toContain("stale");
+
+    const archived = await getJson<Message[]>("/api/messages?archived=1");
+    expect(archived.map((m) => m.body)).toContain("stale");
+  });
+
+  test("clear archives all active messages for everyone", async () => {
+    await post("/api/messages", { from: "a", to: "b", body: "about to be cleared" });
+
+    const response = await handle(new Request("http://test/api/messages/clear", { method: "POST" }));
+    expect(response.status).toBe(200);
+    expect(((await response.json()) as { cleared: number }).cleared).toBeGreaterThanOrEqual(1);
+
+    expect(await getJson<Message[]>("/api/messages")).toEqual([]);
+    expect(await getJson<Message[]>("/api/messages?for=b")).toEqual([]);
+    const archived = await getJson<Message[]>("/api/messages?archived=1&limit=500");
+    expect(archived.map((m) => m.body)).toContain("about to be cleared");
+
+    const fresh = (await (await post("/api/messages", { from: "a", to: "b", body: "after the clear" })).json()) as Message;
+    expect((await getJson<Message[]>("/api/messages?for=b")).map((m) => m.id)).toEqual([fresh.id]);
+  });
+});
+
+describe("web pages", () => {
+  test("setup page shows the install command and chat page has the user form", async () => {
+    const setup = await (await handle(new Request("http://chat.example.com/"))).text();
+    expect(setup).toContain("curl -fsSL http://chat.example.com/install.sh | sh");
+
+    const chat = await (await handle(new Request("http://chat.example.com/chat"))).text();
+    expect(chat).toContain('id="send"');
+    expect(chat).toContain('id="clear"');
+  });
+});
+
 describe("served assets", () => {
   test("skill.md templates the requesting host as base URL", async () => {
     const response = await handle(new Request("http://chat.example.com/skill.md"));