Unified endpoint config type: one Host/IP : Port control in admin

New configSchema type 'endpoint' declared in the module spec: anything
that points at a device or service on the network must be one endpoint
field, rendered identically for every module in /admin as a joined
Host/IP : Port control and stored/handed to the module server as
{ host, port }. Migrates all three connection modules — ProdCom (was a
full URL field), ProPresenter and Timers (were separate host + port
fields). Legacy stored configs (prodcomUrl / flat host+port) keep
working until the admin form is re-saved, at which point the new shape
replaces them. MODULE-GUIDE documents the type and the presentation
rule: no split host/port fields, and full URLs only for genuine web
addresses.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RNYUv9EyrGSFmCnmH7WYKH

README.md

@@ -83,16 +83,16 @@ are written by the app itself.
 - **ProdCom** — live transcript stream with in-place updates of in-progress
   speech, channel colors, per-tile channel visibility toggles and group
   presets, timestamps, text size and jump-to-latest in the title bar.
-  Admin config: ProdCom URL, API key.
+  Admin config: ProdCom server (host : port), API key.
 - **ProPresenter** — what's live and what's next, with slide progress,
   driven by the shared `propresenter-core` client (ProPresenter 7/20).
-  Admin config: host, port, password.
+  Admin config: ProPresenter endpoint (host : port), password.
 - **Timers** — live ProPresenter timers (countdown, countdown-to-time,
   elapsed) and LTC timecode as auto-sized cards. The ＋ picker lists every
   discovered timer (and the LTC card) as its own tile, or add "All timers"
   and pick a selection via the tile's "Timers ▾" menu; overruns are
-  unmistakably red. Read-only — no start/stop controls. Admin config: host,
-  port, password.
+  unmistakably red. Read-only — no start/stop controls. Admin config:
+  ProPresenter endpoint (host : port), password.
 - **Clock** — a big booth clock; also the smallest possible module and the
   reference for module authors.