updatenotify: isolate fork from upstream pfUI traffic + handle dev builds

Switches the addon-message prefix to "pfUI-brues" so we don't share an
inbound queue with upstream pfUI installs at all — they don't register
a listener for this prefix, so our broadcasts get dropped at the engine
level instead of needing branch-string filtering on their end. The
"main" branch tag stays as a tiebreaker for any future fork variant
sharing this prefix.

Source/dev installs leave the toc Version as "@project-version@" until
release tooling substitutes it. pfUI.lua now stamps those as "dev" with
major/minor/fix=0 instead of silently falling back to 1.2.0, and
updatenotify short-circuits on pfUI.version.string == "dev" before
broadcasting so dev installs don't ship a stale low version to everyone
in guild/raid. Single source of truth — the dev marker lives in pfUI.lua.

URLs centralize via the toc's X-Website. updatenotify and firstrun read
it via GetAddOnMetadata + string.format("%s"), and all eight translation
files swap their hardcoded shagu.org references for the same %s slot.

Drive-bys: groupsize math uses ClassicAPI's IsInRaid/IsInGroup; toc
Author typo "modfied" → "modified".

pfUI.toc

@@ -1,12 +1,13 @@
 ## Interface: 11200
 ## Title: |cff33ffccpf|cffffffffUI
-## Author: Shagu - modfied by me0wg4ming & brues
+## Author: Shagu - modified by me0wg4ming & brues
 ## Notes: A complete user interface replacement.
 ## Notes-ruRU: Полная замена пользовательского интерфейса.
-## Version: 8.3.0
+## Version: @project-version@
 ## SavedVariables: pfUI_profiles, pfUI_addon_profiles, pfUI_cache, pfUI_throttle
 ## SavedVariablesPerCharacter: pfUI_config, pfUI_init, pfUI_playerDB
 ## Dependencies: !!!ClassicAPI
+## X-Website: https://github.com/brues-code/pfUI
 
 pfUI.lua