Add bakery.toml and release workflow; improve connect error reporting

- bakery.toml: describes breadcrumbs for bakery install
- release.yml: builds on hestia self-hosted runner, publishes binary to
  dl.breadway.dev and GitHub Releases on v* tags
- flow.rs/nm.rs: connect_and_verify now returns Result<(), String> with
  a descriptive error message instead of a bare bool

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

bakery.toml

@@ -0,0 +1,12 @@
+name = "breadcrumbs"
+description = "Profile-aware Wi-Fi state machine with Tailscale integration"
+binaries = ["breadcrumbs"]
+system_deps = ["networkmanager"]
+bread_deps = []
+
+[config]
+dir = "~/.config/breadcrumbs"
+example = "breadcrumbs.example.toml"
+
+[install]
+post_install = []