feat(notifications): add Pushcut as a notification channel

[MHoroszowski]

Summary

Adds Pushcut as an iOS-native notification channel alongside ntfy, following the existing `sendPush()` pattern in `hooks/lib/notifications.ts`.

Pushcut delivers rich push notifications to iPhone with first-class iOS Shortcuts integration, action buttons, and an Automation Server for unattended Shortcut execution. It's purpose-built for the "webhook → iPhone notification → optional Shortcuts automation" use case.

Why Pushcut

The Apple-native alternative is a custom Apple Push Notification (APNs) integration, which requires:

• Apple Developer account ($99/yr)
• Registered iOS app + provisioning
• APNs certificate management
• Ongoing maintenance every iOS major

Pushcut already runs that infrastructure and exposes it via a single webhook URL. Strictly less complexity for the same delivery guarantees, plus the Shortcuts integration a DIY APNs solution would not provide. The free tier covers most personal notification volumes; Pro is ~$5/mo.

Changes

File	Change
`hooks/lib/notifications.ts`	Add `loadPushcutConfig()` + `sendPushcut()` mirroring the existing ntfy pattern. ~40 lines, no new dependencies.
`settings.json`	Add `notifications.pushcut` block. `enabled: false` by default — opt-in. Reads `PUSHCUT_WEBHOOK_URL` from env via the existing `${VAR}` substitution.

`sendPushcut(message, options)` matches the `sendPush()` signature exactly:

• Fire-and-forget POST
• 5-second timeout via `AbortSignal.timeout`
• Returns `boolean` (true on HTTP 2xx, false on misconfig/error)
• Never throws — failures are silent the same way ntfy failures are

Usage

```ts
import { sendPushcut } from '~/.claude/hooks/lib/notifications';
await sendPushcut('Long task complete', { title: 'Athena' });
```

User setup (will need a docs entry — happy to add to a follow-up doc PR if useful)

1. Install Pushcut from the App Store
2. Create a named notification template in the Notifications tab (the name becomes the URL suffix)
3. Copy the secret webhook URL from the notification's detail view
4. Set `PUSHCUT_WEBHOOK_URL` in `~/.env`
5. Set `notifications.pushcut.enabled = true` in `settings.json`

Test plan

• `sendPushcut()` returns `true` on HTTP 200 from Pushcut API (verified end-to-end — notification arrived on iPhone)
• Returns `false` (no throw) when env var missing or `enabled: false`
• Returns `false` (no throw) on network error or 5s timeout
• Pre-existing `sendPush()` (ntfy) behavior unchanged — same code, same loader pattern
• No new dependencies
• Defaults to `enabled: false` — zero impact on existing installs that don't opt in

Out of scope (intentional, possible follow-ups)

• Multi-channel dispatcher that consults `notifications.routing` — the routing block exists in `settings.json` but no code reads it yet (only individual sender functions are exported). Adding a dispatcher would be a separate, larger PR.
• Pushcut action buttons / defaultAction support — needs a concrete use case to design the API surface. Easy to extend the body shape later without breaking the current signature.
• discord/twilio sender implementations — still settings-only stubs. Independent work.

Related

This is a feature add, not a bug fix. Happy to scope it down further or split if maintainers prefer a smaller initial surface.