Add streaming brotli compression and hot-reloadable config (livevue.toml)

Key changes:

- **src/config.rs** – `LiveVueConfig` (server host/port, brotli quality +
  window size), loaded from `livevue.toml`. A notify-based file watcher
  reloads the config on any file change; a SIGHUP handler does the same on
  demand. Falls back to compiled-in defaults when the file is absent.

- **src/brotli_layer.rs** – `BrotliBody`, a custom `http_body::Body` wrapper
  that streams brotli-compressed data through a single persistent
  `brotli::CompressorWriter`. The encoder survives across SSE event flushes,
  so its sliding window accumulates context from all prior events —
  progressively better compression as the stream grows. Both quality (0–11)
  and window size (lgwin 10–24, i.e. 1 KB – 16 MB) are taken from config.
  `brotli_compression` is an axum `from_fn_with_state` middleware that
  activates only when the client sends `Accept-Encoding: br`.

- **src/server.rs** – `AppState` gains a `config: SharedConfig` field.
  `AppState::new` takes the config; `AppState::new_default` is a zero-config
  convenience constructor.

- **livevue.toml** – documented example config with inline comments
  explaining each field and the brotli window-size tradeoff table.

- **examples/todo** – loads config via `load_and_watch_config`, derives the
  bind address from `config.server`, and applies `brotli_compression` as a
  router layer.

https://claude.ai/code/session_01UnQQkkwts64FPUsSzFfdQb

Cargo.toml

@@ -9,7 +9,7 @@ edition = "2021"
 [features]
 # Opt-in feature: PostgreSQL logical replication for reactive cache invalidation.
 # Adds tokio-postgres and bytes as dependencies.
-pg_replication = ["dep:tokio-postgres", "dep:postgres-protocol", "dep:bytes"]
+pg_replication = ["dep:tokio-postgres", "dep:postgres-protocol"]
 
 [dependencies]
 axum = { version = "0.7", features = ["macros"] }
@@ -25,10 +25,21 @@ tokio-stream = "0.1"
 tracing = "0.1.44"
 futures = "0.3.32"
 
+# Config file parsing
+toml = "0.8"
+
+# Brotli streaming compression (configurable window size + quality)
+brotli = "6"
+pin-project = "1"
+bytes = "1"
+http-body = "1"
+
+# Config file watching (inotify on Linux, kqueue on macOS, FSEvents on macOS)
+notify = "6"
+
 # Optional: PostgreSQL logical replication
 tokio-postgres = { version = "0.7", optional = true }
 postgres-protocol = { version = "0.6", optional = true }
-bytes = { version = "1", optional = true }
 
 [dev-dependencies]
 chrono = { version = "0.4", features = ["clock"] }