Wire breadcrumbs into the bread event fabric (app id crumbs)

The watch daemon publishes bread.crumbs.profile.changed and
bread.crumbs.health.changed on real transitions (not every poll tick)
and honors bread.command.crumbs.set_profile via the existing
state::set_profile path. BreadClient is fail-silent: if breadd is
down, breadcrumbs behaves exactly as before.

Document the contract in EVENTS.md. CLAUDE.md now points at
CONTRIBUTING (single-trunk, no three-branch model), bakery, and
EVENTS.md.

src/state.rs

@@ -2,7 +2,7 @@ use std::fs;
 
 use serde::{Deserialize, Serialize};
 
-use crate::config::{state_dir, state_path};
+use crate::config::{state_dir, state_path, Config};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct State {
@@ -32,3 +32,22 @@ impl State {
         fs::write(state_path(), text).map_err(|e| format!("writing state: {e}"))
     }
 }
+
+/// Persist `name` as the active profile if it exists in `cfg`. Shared by the
+/// CLI `profile set` path and `bread.command.crumbs.set_profile` so they
+/// cannot drift. Does not run [`crate::flow::run`] — the CLI applies
+/// afterwards unless `--no-apply`, and the watch daemon picks the new
+/// profile up on its next tick.
+pub fn set_profile(cfg: &Config, name: &str) -> Result<(), String> {
+    if !cfg.profiles.contains_key(name) {
+        let avail: Vec<&String> = cfg.profiles.keys().collect();
+        return Err(format!("unknown profile '{name}'. Available: {avail:?}"));
+    }
+    State {
+        profile: name.to_string(),
+        updated: crate::util::timestamp(),
+    }
+    .save()?;
+    crate::notify::log(&format!("profile set -> {name}"));
+    Ok(())
+}