Emit bread.paper.changed after a successful set

Link bread-utils v0.7.1 (bread-client) and publish
{ "path": "<wallpaper>" } once awww + wal + bread-theme reload
all succeed. Silent no-op if breadd is down. breadpaper is
CLI-only — no watch subscriber; modules should bread.exec
("breadpaper set …"). See EVENTS.md.

EVENTS.md

@@ -0,0 +1,57 @@
+# breadpaper — bread event integration
+
+breadpaper is a one-shot CLI wallpaper setter: it works exactly the same
+with or without `breadd` running. When breadd *is* present, each successful
+`breadpaper set` (or the bare-path shorthand) publishes one event into the
+shared bread automation fabric. See the parent `bread` repo's
+`Documentation.md` — specifically its "Namespaces" and "Integrating a
+bread\* app" sections — for the general convention this follows.
+
+App id: **`paper`**. Transport: `bread-utils`'s `bread_client` module
+(feature `bread-client`) — the CLI links it directly and uses
+`BreadClient::connect("paper")` + `emit` only. v0.7.1 has no `command()`
+helper, and breadpaper has no long-running process that could hold a
+`subscribe` open.
+
+There is no `breadpaper` daemon and no `watch` subcommand. A `bread-emit
+bread.command.paper.set` (or any other `bread.command.paper.*`) with no
+subscriber is a silent no-op — that is the documented bread convention,
+not a breadpaper bug. Modules that want to change the wallpaper should
+shell out:
+
+```lua
+bread.exec("breadpaper set /path/to/image.png")
+```
+
+The one-shot process still emits `bread.paper.changed` on success, so a
+workflow can `bread.wait("bread.paper.changed", …)` for the real outcome
+instead of assuming the exec finished the set.
+
+## Events published (`bread.paper.*`)
+
+| Event | Data | When |
+|-------|------|------|
+| `bread.paper.changed` | `{ "path": "<wallpaper>" }` | After a successful `set` (awww + wal + `bread-theme reload`). `path` is the canonical absolute path that was applied. Not emitted on `get`, and not emitted if any of the three steps fail. |
+
+## Commands honored (`bread.command.paper.*`)
+
+None, because there is nobody listening.
+
+| Verb | Data | Status |
+|------|------|--------|
+| `set` | `{ "path": "..." }` | **Not subscribed.** The same work is `bread.exec("breadpaper set …")`. A future `breadpaper watch` (or a service-mode of this binary) could honor `bread.command.paper.set` and emit `bread.paper.set.done` / `.failed`; that is deliberately not added here — a long-running process whose only job is to re-exec the existing one-shot CLI is not worth the extra surface. |
+
+### Not implemented: slideshow / library / random / next
+
+breadpaper is not a wallpaper library, a slideshow daemon, or a picker.
+Browsing `~/Pictures/Backgrounds` lives in bos-settings. Do not invent
+`bread.command.paper.next` / `.random` / `.cycle` (or matching events)
+ahead of a real product feature.
+
+## Fail-safe behavior
+
+- If breadd isn't installed or isn't running, `emit` is a silent no-op
+  (`BreadClient::emit` never blocks or errors the caller) — breadpaper
+  still sets the wallpaper, generates the palette, and reloads themes.
+- There is no command subscription to reconnect, because there is no
+  long-running subscriber.