Remote: match the old remote's hardware; old remote code in LEGACY

- LEGACY/remote/teensy/: old remote sketch from
  https://mangavalk.com/Hexapod/remote.git @ 492dece (reference only).
- remote/Config.h: sticks on A0-A5, Nextion on Serial1 (0/1), as in the
  old sketch; MPU6050 moved to Wire2 (25/24) since A4/A5 are Wire's pins.
- NextionUI: controls on a vscope-global "control" page added to the
  old HMI; keeps the old t1 status texts; the old page-1 b2 button (and
  serial 'U') enter Nextion upload passthrough, following the PC's baud.
- Docs: NEXTION.md, remote README wiring, CLAUDE.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-current/remote/NEXTION.md

@@ -1,14 +1,25 @@
 # Nextion HMI build guide
 
-> The owner's earlier 6-page HMI is in `LEGACY/remote/remote.HMI`. This
-> guide describes the minimal single page the current firmware expects.
-> To reuse the old HMI instead, `NextionUI` has to be changed to match
-> its component names.
+Start from your existing HMI (`LEGACY/remote/remote.HMI`, the servo
+monitor) and **add one page named `control`** with the components below.
+Your existing pages keep working:
+
+| Existing | What the firmware does with it |
+|----------|--------------------------------|
+| page 1 `t1`, page 3 `t1` | writes `connected` / `not connected`, as the old firmware did. Set both to **vscope = global**, and put their real names (`page1.t1`, …) in `NEXTION_STATUS_TEXTS` in `Config.h` |
+| page 1 `b2` (id 5) | **upload mode**: keep "Send Component ID" ticked on it. The remote shows `uploadscreen` and passes USB straight through to the display, so Nextion Editor can upload over the remote's USB port. Power-cycle to leave. Serial key `U` does the same |
+| page 4 `uploadscreen` | shown on entering upload mode |
+| page 3 sliders `h0`–`h17` | not driven yet: the robot doesn't send servo positions back (that needs the planned telemetry channel) |
 
 The firmware drives the display by **component name**, and the display
 talks back with small custom frames sent from each button's touch event.
-Build one page in Nextion Editor to match the tables below. Layout, fonts
-and colors are up to you. The names and event code must match exactly.
+Layout, fonts and colors are up to you. The names and event code must
+match exactly.
+
+**Set every component on `control` to vscope = global.** The firmware
+writes them as `control.<name>` and keeps them current whichever page is
+showing. A local component on another page can't be written from outside,
+and with `bkcmd=0` the display ignores those writes silently.
 
 The remote is authoritative. Use **plain Button** components (not
 Dual-state buttons) and don't toggle anything locally in the HMI. The
@@ -24,9 +35,13 @@ bauds=115200
 ```
 
 This sets the display to the `NEXTION_BAUD` in `remote/Config.h`. The
-display ships at 9600, and `bauds=` persists across power cycles.
+display ships at 9600, and `bauds=` persists across power cycles. The old
+firmware used the ITEAD library at 9600, so your HMI probably runs at 9600
+today.
 
-Name the page `main` (page 0). The firmware never changes pages.
+Name the new page `control`. The firmware never changes pages, except
+into `uploadscreen` for upload mode. Add buttons on your other pages to
+switch to it (`page control`).
 
 ## Components
 
@@ -75,8 +90,9 @@ uses **Touch Move** as well so the value tracks your finger). Frame format:
 | `bCal`    | `printh 23 01 43`                        | `C` start / save stick calibration |
 | `bCalX`   | `printh 23 01 51`                        | `Q` cancel calibration         |
 
-**Uncheck "Send Component ID"** on every component. The firmware ignores
-standard touch frames, and they only add serial traffic.
+**Uncheck "Send Component ID"** on every component on `control`: those
+standard touch frames only add serial traffic. The one exception is the old
+page 1 `b2` upload button (see the top).
 
 Protocol details and the parser live in `NextionUI.h/.cpp`. To add a
 control, pick an unused command byte, add it to `NextionUI::decodeCustom()`