Give the dock its own compact notes layout

The dock was showing `NotesPanel`, which is a master/detail layout: a column
of titles beside an editor. The previous commit made that survive dock width;
it did not make it right. At 352px the layout still spends roughly 356px of
height on chrome — dock header, panel header, title strip, a button row that
wraps, and a paragraph of help — before the body gets a pixel.

So the dock now shows one note. The title field names what is open and the
chevron beside it switches; New and Delete move into the overflow menu; the
help text goes. Chrome drops to about 112px and the body takes the rest.

The two surfaces are now different components, which contradicts a docstring
I wrote — "shared so the two cannot drift into different behaviour". That
claim was about behaviour, and behaviour was never in the layout: it is in
`useNotes` for the cache and its write ordering, and now in `useNoteDraft`,
extracted here so when a keystroke becomes a save is defined in exactly one
place. Only the layout diverges. `NotesPanel.shared.test.tsx` gets stronger
for it — it now mounts the dock panel and the tab panel together, which is
what the app actually does, instead of the same component twice.

`NoteSwitcher` is not `OverflowMenu` despite the shape being close: that keys
items by label, and notes are addressed by id, so two untitled notes — the
ordinary case — would collapse into one row. It is also not a `combobox`; an
input plus a listbox button is two honest controls, where the role would owe
active-descendant tracking and filtering that nothing here needs.

`SendToAgentButton` picks up `useUnavailable` from #49, which is what its
`disabled` plus explanatory `title` was already asking for. Four tests moved
from `toBeDisabled()` to the new contract, and one of them — "does nothing for
an empty note" — turned out never to have asserted that it does nothing. It
does now, for click and for Enter, which is the guard the swap needs.

It also gains `dropUp`, and that is load-bearing rather than cosmetic: the
dock clips its own overflow, so a session menu opening downward from a button
on the bottom edge is drawn outside the panel and never seen.

744 tests pass, 62 files. As before, jsdom has no layout engine: that the dock
now reads as compact is not something the suite can tell you.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011YPqHpjV4EL6RNEwrRKqQm

app/src/components/notes/NotesDockPanel.tsx

@@ -0,0 +1,119 @@
+import { useMemo, useState } from "react";
+import { useNotes } from "../../hooks/useNotes";
+import { useNoteDraft } from "./useNoteDraft";
+import NoteSwitcher from "./NoteSwitcher";
+import SendToAgentButton from "./SendToAgentButton";
+import Button from "../ui/Button";
+import OverflowMenu from "../ui/OverflowMenu";
+import SaveIndicator from "../ui/SaveIndicator";
+
+interface Props {
+  projectId: string;
+}
+
+/**
+ * Notes at dock width.
+ *
+ * Deliberately not `NotesPanel` in a narrower box. The tab can afford a column
+ * of titles beside the editor; the dock cannot, and shrinking that layout
+ * spends its height on chrome — a title strip, a wrapped button row and a
+ * paragraph of help — for a body that ends up a few words wide.
+ *
+ * So the dock shows exactly one note. The title row names it and switches to
+ * another, the actions that are not writing live in the overflow menu, and
+ * everything left over is the body. Roughly 240px of height comes back.
+ *
+ * What the two surfaces share is the part that must not drift: `useNotes` for
+ * the cache and its write ordering, and `useNoteDraft` for when a keystroke
+ * becomes a save. Only the layout is different.
+ */
+export default function NotesDockPanel({ projectId }: Props) {
+  const { notes, loading, saveState, createNote, saveNote, deleteNote } =
+    useNotes(projectId);
+  const [selectedId, setSelectedId] = useState<string | null>(null);
+
+  const selected = useMemo(
+    () => notes.find((n) => n.id === selectedId) ?? notes[0] ?? null,
+    [notes, selectedId],
+  );
+
+  const { title, body, setTitle, setBody, commit } = useNoteDraft(
+    selected,
+    saveNote,
+  );
+
+  const onCreate = async () => {
+    const note = await createNote();
+    if (note) setSelectedId(note.id);
+  };
+
+  if (loading) {
+    return (
+      <p className="p-4 text-xs text-[var(--text-secondary)]">Loading notes…</p>
+    );
+  }
+
+  if (!selected) {
+    return (
+      <div className="flex-1 flex flex-col items-center justify-center gap-3 p-4">
+        <p className="text-[13px] text-[var(--text-secondary)] text-center">
+          Keep reminders here, and send any of them straight to a running Claude
+          session.
+        </p>
+        <Button variant="primary" onClick={onCreate}>
+          New note
+        </Button>
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex flex-col h-full min-h-0">
+      <div className="flex items-center gap-1 px-2 py-1.5 flex-shrink-0 border-b border-[var(--border-color)]">
+        <div className="flex-1 min-w-0">
+          <NoteSwitcher
+            notes={notes}
+            selectedId={selected.id}
+            title={title}
+            onTitleChange={setTitle}
+            onCommit={commit}
+            onSelect={setSelectedId}
+          />
+        </div>
+        {/* Renders nothing while idle, so it costs no width until it matters. */}
+        <SaveIndicator state={saveState} />
+        <OverflowMenu
+          label="Note actions"
+          items={[
+            { label: "New note", onSelect: () => void onCreate() },
+            {
+              label: "Delete note",
+              danger: true,
+              onSelect: () => void deleteNote(selected.id),
+            },
+          ]}
+        />
+      </div>
+
+      <textarea
+        value={body}
+        onChange={(e) => setBody(e.target.value)}
+        onBlur={commit}
+        placeholder="Reminders, gotchas, a prompt worth keeping…"
+        aria-label="Note body"
+        className="flex-1 min-h-0 w-full px-3 py-2 bg-transparent text-[13px] text-[var(--text-primary)] resize-none font-mono"
+      />
+
+      <div className="px-2 py-2 flex-shrink-0 border-t border-[var(--border-color)]">
+        {/* The live draft, not `selected.body` — what is on screen is what gets
+            sent. `dropUp` because the dock clips its own overflow. */}
+        <SendToAgentButton
+          projectId={projectId}
+          body={body}
+          fullWidth
+          dropUp
+        />
+      </div>
+    </div>
+  );
+}