Establish config loading and logging infrastructure

First working milestone of the Rust rewrite. Implements the two
foundational systems every other component depends on:

- TOML-based layered config (beds.toml + env.toml override) replacing
  the PHP XML config system, fully deserialized into typed structs via
  serde — no runtime string key lookups, shape enforced at compile time
- Structured logging via tracing + tracing-journald, with optional
  console mirror, initialized from config before any services start

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

.gitignore

@@ -1 +1,2 @@
 /target
+config/env.toml