feat: PING watchdog, IRCv3 server-time, push notifications

PING watchdog sends PING after configurable silence interval and
disconnects on timeout, detecting stale connections that TCP alone
misses. IRCv3 server-time capability is requested on every connection;
timestamps are injected on dispatch and backlog replay for clients
that support message tags. Push notifications via ntfy or generic
webhook fire on highlights and PMs when no clients are attached,
with configurable cooldown and optional SOCKS5 routing.

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

docs/USAGE.md

@@ -171,6 +171,83 @@ replay_on_connect = true   # set false to disable replay
 
 Stored commands: `PRIVMSG`, `NOTICE`, `TOPIC`, `KICK`, `MODE`.
 
+## PING Watchdog
+
+The bouncer sends periodic PING messages to detect stale server connections
+(socket open but no data flowing). If no data is received within the configured
+interval, a PING is sent. If the server doesn't respond within the timeout,
+the connection is dropped and a reconnect is scheduled.
+
+```toml
+[bouncer]
+ping_interval = 120   # seconds of silence before sending PING
+ping_timeout = 30     # seconds to wait for PONG after PING
+```
+
+The watchdog starts automatically when a network enters the READY state.
+Any received data (not just PONG) resets the timer.
+
+## IRCv3 server-time
+
+The bouncer requests the `server-time` IRCv3 capability on every connection.
+When enabled by the server, timestamps on incoming messages are preserved and
+forwarded to clients. When the server does not provide a timestamp, the bouncer
+injects one using the current UTC time.
+
+Backlog replay also includes timestamps from when messages were originally
+stored, so clients that support `server-time` see accurate times on replayed
+messages.
+
+No client configuration is needed -- timestamps appear automatically if the
+client supports IRCv3 message tags.
+
+## Push Notifications
+
+When no IRC clients are connected to the bouncer, highlights and private
+messages can trigger push notifications via [ntfy](https://ntfy.sh) or a
+generic webhook.
+
+### Setup
+
+```toml
+[bouncer]
+notify_url = "https://ntfy.sh/my-bouncer-topic"
+notify_on_highlight = true    # mentions of your nick in channels
+notify_on_privmsg = true      # private messages
+notify_cooldown = 60          # min seconds between notifications
+notify_proxy = false          # route notifications through SOCKS5
+```
+
+### ntfy Example
+
+```toml
+notify_url = "https://ntfy.sh/my-secret-topic"
+```
+
+Install the ntfy app on your phone and subscribe to the topic. Notifications
+include the sender, target, and message text.
+
+### Generic Webhook
+
+Any URL that does not contain `ntfy` in the hostname is treated as a generic
+webhook. The bouncer POSTs JSON:
+
+```json
+{
+  "network": "libera",
+  "sender": "user",
+  "target": "#channel",
+  "text": "hey mynick, check this out"
+}
+```
+
+### Behavior
+
+- Notifications only fire when **no clients** are attached
+- The cooldown prevents notification floods (one per `notify_cooldown` seconds)
+- When `notify_proxy = true`, notification requests are routed through the
+  configured SOCKS5 proxy
+
 ## Configuration Reference
 
 ```toml
@@ -199,6 +276,17 @@ email_request_timeout = 20 # per-request timeout for email APIs
 # Certificate generation
 cert_validity_days = 3650  # client cert validity (~10 years)
 
+# PING watchdog
+ping_interval = 120        # seconds of silence before sending PING
+ping_timeout = 30          # seconds to wait for PONG after PING
+
+# Push notifications
+notify_url = ""            # ntfy or webhook URL (empty = disabled)
+notify_on_highlight = true # notify on nick mentions
+notify_on_privmsg = true   # notify on private messages
+notify_cooldown = 60       # min seconds between notifications
+notify_proxy = false       # route notifications through SOCKS5
+
 [bouncer.backlog]
 max_messages = 10000       # per network, 0 = unlimited
 replay_on_connect = true   # replay missed messages on client connect