deploy: no deployer for Espressif8266, so ESP8266 boards build but cannot be flashed #1657

Summary

fbuild build works for ESP8266 boards, and the CI badge shows ESP8266 builds
passing. fbuild deploy for the same environment fails before opening the port:

deployer for Espressif8266 not yet implemented

On main the deploy dispatch in
crates/fbuild-daemon/src/handlers/operations/deploy.rs has arms for
Espressif32, AtmelAvr/AtmelMegaAvr, Teensy, RaspberryPi, NxpLpc and
Ch32v. Espressif8266 falls through to the _ arm.

Reproduction

• Host: Windows 11, fbuild 2.5.26. The dispatch is unchanged on main as of
  2026-10-07 (2.5.37).
• Board: nodemcuv2, Arduino framework.
• fbuild build -e <env> succeeds. A sketch of ours builds to 270,961 bytes of
  flash.
• fbuild deploy -e <env> -p COM255 --skip-build fails with the message above.
  COM255 does not exist; the error comes from the platform dispatcher before
  any port is opened.

Impact

Design Studio for FastLED drives fbuild as one of its two build engines. For
ESP8266 it detects this message and tells the user to switch to the arduino-cli
engine to upload. So an ESP8266 project can build on fbuild, but can only be
flashed with the other engine.

Suggestion

esptool already supports the ESP8266 (--chip esp8266). Since 2.5.31 (#1618)
the ESP32 deployer spawns the build-resolved esptool. An ESP8266 deployer could
probably follow the same path with the ESP8266 chip, its flash layout and the
usual DTR/RTS auto-reset that NodeMCU and D1 Mini boards use.

If a deployer is not planned, an error that names the gap would still help, for
example "ESP8266 boards can be built but not deployed by fbuild yet". Today's
message reads like an internal failure.

We can test a build on a Windows host.