feat(core): A.6.1 — use OS connectivity signals to drive reconnect

Extends the A.6 supervisor with an OS-level connectivity hint so a
returning network triggers a redial immediately instead of waiting
out the current backoff slot (up to 60 s). The watchdog remains the
authoritative loss detector — the OS signal is advisory.

* `chanora_core::NetworkState` (Unknown / Online / Offline) is owned
  by `ChanoraSession` via a `tokio::sync::watch::Sender`.
  `set_network_state()` / `network_state()` are the public accessors.
* The supervisor's watch-phase `select!` gains a `network_rx`
  branch: Offline pre-charges watchdog misses (capped at
  `MAX_MISSES - 1`) so the next probe failure trips immediately;
  Online clears stale misses. This shrinks UI-banner latency on a
  Wi-Fi drop from ~15 s to ~5 s.
* The reconnect-loop's backoff sleep races against Online: a
  transition cuts the sleep short and resets the attempt counter so
  future losses start at the smallest backoff window again.
* `chanora_bridge` adds `BridgeNetworkState` (mirror enum) and a
  sync `set_network_state(state)` function. On platforms with no
  signal wired the supervisor stays at Unknown and falls back to
  pure watchdog/backoff — no behavioural regression vs A.6.
* Flutter adds `connectivity_plus ^6.1.0` and wires
  `_wireConnectivity()` in `main()`: seeds with `checkConnectivity()`
  then forwards every `onConnectivityChanged` to the bridge,
  mapping any non-`none` transport to Online.

Verified on Moto G Stylus 5G (Android 14): `svc wifi disable && svc
data disable` for ~40 s — reconnect banner appeared promptly
because the watchdog was pre-charged. After `svc wifi enable && svc
data enable` the supervisor woke from its 15 s backoff slot and
reconnected within seconds; the channel tree re-rendered without
user action.

apps/chanora_flutter/pubspec.lock

@@ -129,6 +129,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.19.1"
+  connectivity_plus:
+    dependency: "direct main"
+    description:
+      name: connectivity_plus
+      sha256: b5e72753cf63becce2c61fd04dfe0f1c430cc5278b53a1342dc5ad839eab29ec
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.1.5"
+  connectivity_plus_platform_interface:
+    dependency: transitive
+    description:
+      name: connectivity_plus_platform_interface
+      sha256: "3c09627c536d22fd24691a905cdd8b14520de69da52c7a97499c8be5284a32ed"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.0"
   convert:
     dependency: transitive
     description:
@@ -161,6 +177,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.1.7"
+  dbus:
+    dependency: transitive
+    description:
+      name: dbus
+      sha256: d0c98dcd4f5169878b6cf8f6e0a52403a9dff371a3e2f019697accbf6f44a270
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.12"
   fake_async:
     dependency: transitive
     description:
@@ -169,6 +193,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.3.3"
+  ffi:
+    dependency: transitive
+    description:
+      name: ffi
+      sha256: "6d7fd89431262d8f3125e81b50d3847a091d846eafcd4fdb88dd06f36d705a45"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.2.0"
   file:
     dependency: transitive
     description:
@@ -216,6 +248,11 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_web_plugins:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   freezed:
     dependency: "direct dev"
     description:
@@ -360,6 +397,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.0.0"
+  nm:
+    dependency: transitive
+    description:
+      name: nm
+      sha256: "2c9aae4127bdc8993206464fcc063611e0e36e72018696cd9631023a31b24254"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.5.0"
   package_config:
     dependency: transitive
     description:
@@ -376,6 +421,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.9.1"
+  petitparser:
+    dependency: transitive
+    description:
+      name: petitparser
+      sha256: "91bd59303e9f769f108f8df05e371341b15d59e995e6806aefab827b58336675"
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.0.2"
+  plugin_platform_interface:
+    dependency: transitive
+    description:
+      name: plugin_platform_interface
+      sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.8"
   pool:
     dependency: transitive
     description:
@@ -541,6 +602,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.0.3"
+  xml:
+    dependency: transitive
+    description:
+      name: xml
+      sha256: "971043b3a0d3da28727e40ed3e0b5d18b742fa5a68665cca88e74b7876d5e025"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.6.1"
   yaml:
     dependency: transitive
     description: