fix(app): source composer cwd from agent state, not draft hook

The GitHub picker showed "No results found." for any running agent after
the first message was sent. useAgentInputDraft owned a local cwd state
that clear("sent") wiped to "", so the composer read cwd: "" even though
the agent's real cwd was correct on the wire.

Drop cwd ownership from the hook. Composer takes cwd as a prop sourced
by the parent — agentState.cwd for running agents, composerState.workingDir
for drafts, sourceDirectory for setup flows. The hook now persists only
{text, attachments}. Legacy persisted drafts with a cwd field still
hydrate; tagged COMPAT(draft-cwd) for removal after 2026-11-09.

Also moves attachment pills back inside the composer's bordered surface
via a new attachmentSlot prop on MessageInput, and shrinks pill height
from 48 to 32 — the subagents-track tuck previously had attachments
floating between it and the input.

Adds one Playwright spec asserting the draft-create-agent path submits
the workspace cwd.

packages/app/src/stores/draft-store.lifecycle.test.ts

@@ -7,19 +7,19 @@ describe("draft-store lifecycle", () => {
     const nowMs = 1_000_000;
     const drafts = {
       oldSent: {
-        input: { text: "", attachments: [], cwd: "" },
+        input: { text: "", attachments: [] },
         lifecycle: "sent" as const,
         updatedAt: 0,
         version: 2,
       },
       recentAbandoned: {
-        input: { text: "", attachments: [], cwd: "" },
+        input: { text: "", attachments: [] },
         lifecycle: "abandoned" as const,
         updatedAt: nowMs + 2 * 60 * 1000,
         version: 2,
       },
       active: {
-        input: { text: "a", attachments: [], cwd: "/repo" },
+        input: { text: "a", attachments: [] },
         lifecycle: "active" as const,
         updatedAt: 0,
         version: 1,
@@ -53,7 +53,6 @@ describe("draft-store lifecycle", () => {
               },
             },
           ],
-          cwd: "/repo",
         },
         lifecycle: "active",
         updatedAt: 1,
@@ -64,7 +63,7 @@ describe("draft-store lifecycle", () => {
     });
 
     expect(cleared).toEqual({
-      input: { text: "", attachments: [], cwd: "" },
+      input: { text: "", attachments: [] },
       lifecycle: "sent",
       updatedAt: 2,
       version: 2,