feat(mac-client): Lisa.app native Mac client for the chat GUI

[oratis]

Closes #25. Sibling to LisaIsland.app — same WKWebView wrapper pattern, but for the full chat GUI rather than the always-on-top pill.

Why a separate app

	LisaIsland.app	Lisa.app (this PR)
What it is	Passive observer	Active conversation
Dock icon	✗	✓ (mascot)
Window chrome	borderless, transparent	standard (titlebar, traffic lights)
Z-order	always on top	normal; ⌘Tab works
Loads	`/island`	`/` (chat GUI)
When to use	Always running in background	Open when you want to chat
Activation policy	`.accessory`	`.regular`

Install one, both, or neither. Both just hit `localhost:5757`; neither knows about the other.

What's in this PR

`packaging/mac-client/` — a SwiftPM target that produces `Lisa.app`:

```
Sources/Lisa/
├── main.swift 19 LOC NSApplication boot (.regular policy)
├── AppDelegate.swift 175 LOC window lifecycle + standard menu bar
├── MainWindow.swift 55 LOC NSWindow + frame autosave
└── WebContent.swift 94 LOC WKWebView + auto-retry + external links

### App icon generated at build time

\`build.sh\` runs \`sips\` + \`iconutil\` against the existing
\`src/web/assets/lisa-mascot.png\` (1024×1024) to produce the
\`.iconset\` then \`.icns\`. No binary blobs committed; the icon stays
in sync if the mascot changes.

### Standard menu bar

| Shortcut | Action |
|---|---|
| ⌘N | New / show window |
| ⌘W | Close window (app stays in Dock) |
| ⌘R | Reload chat |
| ⌘F | Toggle fullscreen |
| ⌘M | Minimize |
| ⌘H | Hide |
| ⌘Q | Quit |

### Frame autosave

NSWindow's \`frameAutosaveName\` is set to \`ai.meetlisa.app.MainWindow\`,
so window position + size persist across launches. Defaults to 1200×800
centered on first run.

### External links

\`target=_blank\` links inside the chat (e.g. someone shares a URL)
open in the user's default browser via \`NSWorkspace.shared.open\`
rather than spawning a new in-app WebView.

## Verified locally

✓ \`bash build.sh\` succeeds; produces universal binary (arm64 + x86_64)
✓ \`Lisa.app/Contents/Resources/AppIcon.icns\` generated (~1 MB)
✓ App launches; mascot icon appears in Dock
✓ Two ESTABLISHED connections to localhost:5757 (page + \`/events\` SSE)
✓ \`⌘W\` closes window; \`⌘Q\` quits; Dock click reopens after \`⌘W\`
✓ \`⌘R\` reloads
✓ Runs simultaneously with LisaIsland.app — both reach LISA independently

## Verification

\`\`\`sh
lisa serve --web
cd packaging/mac-client
bash build.sh
open Lisa.app
\`\`\`

## Out of scope

- Multi-window — single window for now
- URL scheme integration with LisaIsland (\`open_full_gui\` could deep-link to Lisa.app instead of opening Safari) — separate small PR if/when desired
- Native menu commands talking to LISA's REST endpoints — separate small PRs (\`⌘N\` → \`POST /api/birth\` for new soul, etc.)
- Apple Developer ID signing + notarization + Homebrew Cask — Phase 4 of MAC_ISLAND_PLAN

## Diff stat

| File | LOC |
|---|---|
| \`Sources/Lisa/*.swift\` | 343 |
| \`Package.swift\` | 13 |
| \`Resources/Info.plist\` | 45 |
| \`build.sh\` | 109 |
| \`README.md\` | 101 |
| \`.gitignore\` | 14 |
| **Total** | **625** |

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