feat: reactions, link previews, mobile layout, TUI multi-network + /react usage hints

- TUI /react shows usage hint on bad/missing args instead of silently no-oping
- README: document /join /net /react slash commands and Ctrl+N keybinding
- README: add send_reaction IPC command and reaction IPC event to protocol reference
- FUTURE.md: mark reactions, link previews, responsive mobile layout, TUI
  multi-network and TUI reactions as shipped; add prose sections for each
- EXTENSIONS.md: add EXT-008 documenting reaction wire protocol, SQLite
  schema, IPC commands/events, history replay, and browser-mode implementation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

FUTURE.md

@@ -137,9 +137,25 @@ Web frontend (React, already built) + [Wails v2](https://wails.io) shell for nat
 | ✅ shipped | P2P message history gossip (EXT-007) — new peers receive recent history from first connected peer |
 | ✅ shipped | Date-aware timestamps in TUI and web UI |
 | ✅ shipped | Historical peer alias resolution in web UI |
+| ✅ shipped | Message reactions (emoji picker, full-stack: wire protocol, SQLite, IPC, web UI, TUI) |
+| ✅ shipped | Link rendering + image preview in web UI messages |
+| ✅ shipped | Responsive mobile layout (slide-over sidebar, hamburger button) |
+| ✅ shipped | TUI multi-network (join/switch networks at runtime, `ctrl+n`, `/join`, `/net`) |
+| ✅ shipped | TUI message reactions (`/react <emoji>` or `/react <n> <emoji>`) |
 | 🔜 planned | Push notifications (PWA Web Push + service worker) |
-| 🔜 planned | Message reactions (emoji, full-stack gossip) |
-| 🔜 planned | Link rendering + image preview in messages |
+
+### Message Reactions ✅ (shipped)
+Full-stack emoji reactions. The web UI shows a `+` button on hover that opens a six-emoji picker (👍 ❤️ 😂 😮 😢 🙏). Reactions render as chips below each message; clicking an existing chip toggles your own reaction. Reactions are stored in SQLite (`reactions` table), gossiped over the mesh as `reaction` wire messages (EXT-008), and replayed via IPC on reconnect.
+
+Browser mode: `browser.ts` independently mirrors the daemon — reactions flow over the DataChannel and are broadcast to all connected peers.
+
+TUI: messages show `[n]` line numbers. Use `/react <emoji>` (reacts to last message) or `/react <n> <emoji>` (reacts to message `n`). Reactions render inline below the target message.
+
+### Link Rendering + Image Preview ✅ (shipped)
+URLs in messages are auto-linked. URLs ending in a recognized image extension (`.jpg`, `.png`, `.gif`, `.webp`, `.svg`) render an inline `<img>` preview (max 320×200px). `blob:` and `data:image` URLs are also treated as images.
+
+### Responsive Mobile Layout ✅ (shipped)
+At viewport width ≤ 600px the sidebar becomes a fixed-position slide-over drawer, hidden off-screen by default (`transform: translateX(-100%)`). A `☰` hamburger button in the message pane header toggles it open. Clicking any room or network in the sidebar closes it automatically. The layout is dimmed while the sidebar is open via a `::before` overlay.
 
 ### Push Notifications (planned)
 The web UI is already a PWA (installable, has manifest). The missing half is a service worker + Web Push subscription: