Stacks: one machine, one set of files; default home is <data dir>/stacks

The hub no longer probes a node's Docker on tcp :2375, holds compose files
for a node, or runs compose against another machine's Docker. hubStacks,
nodeDocker, taskOnHub and the hub-side /api/nodes/{node}/docker/... routes
are gone; the generic node proxy hands those requests to the node's own
Ham Lab. Stack.remote / held_by and compose.Spec.Remote are removed.

New stacks default to <data dir>/stacks on every machine. Folders with two
or more deployed stacks are still offered, after it, never as default.
The ~/stacks fallback is gone. A missing home is skipped without a sudo find.

A schedule saved earlier with a tcp target is refused with a message
instead of being run against this machine's Docker.

PORTABILITY.md 3.1, 3.2, 3.3 and 9.2 done; 3.5 checked, no change needed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/StackNew.tsx

@@ -101,7 +101,7 @@ export default function StackNew({ mode, from, networks = [], taken, onClose, on
           {homes.length > 1 && <label className="muted">Where
             <select value={home} onChange={(e) => setHome(e.target.value)}>{homes.map((h) => <option key={h.dir + h.via} value={h.dir}>{sameTail(h) ? h.dir : tail(h.dir)} · {h.stacks} stack{h.stacks === 1 ? '' : 's'}</option>)}</select>
           </label>}
-          {picked && <div className="muted small mono" style={{ overflowWrap: 'anywhere' }}>{picked.dir}/{name || '…'}/compose.yaml{picked.held_by && ` — kept on ${picked.held_by}, deployed here over ${picked.remote}`}{picked.via && ` — compose runs inside ${picked.via}, like its neighbours`}</div>}
+          {picked && <div className="muted small mono" style={{ overflowWrap: 'anywhere' }}>{picked.dir}/{name || '…'}/compose.yaml{picked.via && ` — compose runs inside ${picked.via}, like its neighbours`}</div>}
           {!from && <div className="tabs"><button className={how === 'form' ? 'on' : ''} onClick={() => setHow('form')}>Form</button><button className={how === 'compose' ? 'on' : ''} onClick={toCompose}>Compose</button></div>}
           {how === 'form' ? <>
             <label className="muted">Image<input className="mono" value={form.image} onChange={set('image')} placeholder="traefik/whoami:latest" spellCheck={false} autoCapitalize="off" autoCorrect="off" /></label>