Removed reference to APRS interoperability with APRS.

When the APRS channel is selected, the input placeholder shows
'@callsign message  or  #group message ...' so users know the
direct-message and group syntax without reading docs.

- aprs.process() was empty, so outbound messages from UI never reached
  APRS-IS. Now calls send() for locally-originated messages.
- Regex for parsing message IDs didn't handle APRS 1.1 reply-ack
  trailing '}', causing {01} to appear in message text and ACKs
  not being sent back (Xastir kept retransmitting).

…eed channel

- Inbound messages from callsigns with a DM channel (e.g. kj6dzb-4 og==)
  now route to that DM channel instead of always going to the group feed.
- Group members always route to the main APRS feed channel.
- Outbound from DM channels auto-routes to the callsign in the channel
  name, stripping redundant @callsign prefix if present.
- Default feed channel renamed to APRS-IS-Feed (no spaces in namekey).
- Feed channel is auto-registered at setup even if not in config.
- Channel key extracted once at setup for efficient DM matching.

…nly, wire up gatekeeper ref in meshcore

- meshcore.uc: accept gatekeeper reference from config, add early-drop comment for encrypted packets
- router.uc: when gatekeeper strict, only bridge text_message outbound to MeshCore and Meshtastic
- Remove old r12 package artifacts

ucode is not JavaScript — it has no global 'undefined'. Unset
properties return null. Using '!== undefined' caused a runtime
Reference error crashing /join when putGroup() or setLocalChannel()
was called.

Fixed in groups.uc putGroup() and channel.uc setLocalChannel().

The og== key is what marks a channel as AREDN-only, not the %
prefix. Converting #me to %me confused users. Now /join #me CALL1
msg creates '#me og==' — the name the user typed, with the
AREDN-only key.

- /channels world: show 'Requesting...' feedback when bridge found,
  show 'No bridge available' when none exists (was silent)
- /backend: alias to /backends (user tried singular form, got nothing)
- Unknown commands: reply with helpful error instead of silent drop
- process() reply_public_channels: add missing break before default

Two issues prevented outbound messages from group channels:

1. /join without explicit backend= never registered the channel in
   channelBackendMap, so process() silently dropped outbound messages.
   Now always binds to default backend.

2. Plain text in a group channel (e.g. #me) was sent to default_group
   instead of the channel's own group. Now resolves the group from
   the channel name first, falling back to default_group.

updateChannelBackend(namekey, null) from /join (no explicit backend)
was hitting the 'explicitly cleared' branch and removing the channel
from channelBackendMap. Now null means 'bind to default' and only
empty string means 'explicitly clear'.

- Channel names keep user's prefix (no more # to % swap)
- Callsign detection requires at least one digit
- Group channels auto-bound to default backend for outbound
- Sidebar strips # and % from display labels
- Fix typo ARSDN → AREDN

New slash command to export the current channel's messages as a
downloadable file:
  /export       — plain text log (default)
  /export csv   — CSV with timestamp, from, message columns
  /export text  — plain text log

Server collects messages, formats them, and sends a /export event.
UI triggers a browser file download with the formatted data.
Filenames use channel name + timestamp, e.g. TacNet-20260604-220900.txt

ucode arrays don't support arbitrary property assignment — setting
_namekey on the command array was silently dropped, causing /export
to always show 'No channel selected'.

Xastir and YAAC 'Server Ports' emulate APRS-IS tier-two servers
and require the standard login handshake with a valid passcode
for write access. Without it, the connection is read-only and all
injected traffic is silently dropped.

Now all text-based backend types (aprsis, tcp_text, xastir, yaac)
send the login handshake on connect. The passcode field is optional
— omitting it or setting -1 gives receive-only access.

Also updated APRS.md with passcode documentation.

TCP connect to an unreachable mesh IP blocks the entire event loop
(default SYN timeout ~75s+). Sets SO_SNDTIMEO before connect to
fail fast, then clears it after successful connect.

Also added xastir_dzb4 backend (tcp_text) to docs and example config.
All text-based backends now send APRS-IS login handshake with passcode.

SO_SNDTIMEO doesn't work for connect timeout in ucode's socket API.
Switch to SOCK_NONBLOCK with async connect completion check:
- connect() returns immediately with EINPROGRESS
- handle() polls SO_ERROR to detect completion
- 10s deadline auto-retries with exponential backoff
- Prevents unreachable mesh IPs from blocking entire event loop

- Add APRS-IS login handshake for tcp_text/xastir/yaac backends
- Fix: add 5s connect timeout to prevent blocking on unreachable backends
- Fix: non-blocking connect for APRS backends
- Fix: use time() instead of now() in checkPendingConnect (scope issue)

Added new features guides for APRS bridge and Strict Gatekeeper mode.