webui: add a device hostname and access point table

[MUSTARDTIGERFPV]

Closes #528.

elrs_tx.local and elrs_rx.local are documented well. elrs_txbp.local and elrs_vrx.local appear on the Backpack pages. elrs_aat.local and elrs_timer.local do not appear anywhere on the site. There is also no single place that lists them, so a user setting up a Backpack has to guess or go searching.

This adds one table at the end of "How to get to the Web UI".

Device	Hostname	Access Point
Transmitter module	elrs_tx.local	ExpressLRS TX
Receiver	elrs_rx.local	ExpressLRS RX
TX Backpack	elrs_txbp.local	Changes with the selected service
VRx Backpack	elrs_vrx.local	ExpressLRS VRx Backpack
Antenna Tracker Backpack	elrs_aat.local	ExpressLRS AAT Backpack
Timer Backpack	elrs_timer.local	ExpressLRS Timer Backpack

Sources

Everything is taken from source rather than from existing docs.

• elrs_tx / elrs_rx and the ExpressLRS TX / ExpressLRS RX access point names are in src/lib/OPTIONS/options.cpp in this firmware repo, along with wifi_ap_password = "expresslrs" and wifi_ap_address = "10.0.0.1".
• elrs_aat, elrs_vrx, elrs_txbp and elrs_timer and their access point names are in lib/WIFI/devWIFI.cpp in the Backpack repository, selected by AAT_BACKPACK, TARGET_VRX_BACKPACK, TARGET_TX_BACKPACK and TARGET_TIMER_BACKPACK.
• The TX Backpack is the one exception. Its SSID is static char wifi_ap_ssid[33] and is filled in at runtime from the selected wifiService, so the table says it changes rather than naming a fixed string.
• The Backpack uses the same expresslrs password and the same 10.0.0.1 address (static IPAddress apIP(10, 0, 0, 1)).

Word list

Adds DHCP, MDNS, VRx, hostname and hostnames.

These terms are already used across the site, but every existing occurrence sits inside an admonition body. The spellcheck's markdown filter loads only markdown.extensions.extra, so those indented blocks are parsed as code blocks and skipped. The new table is top level prose, so the words are checked for the first time.

VRx is kept in that exact mixed case because it is the literal SSID string the user sees when picking a network.