docs: add BACKLOG.md and RELEASE_PLAN_v4.6.0.md

Backlog: legacy 'queit' removal, dead /RGB suffix, #RRGGBB hex parsing,
PID channel type, SPI CAN controller, T:99 rotary profiles, ESP32 PWM stub,
doc/site work. Release plan: v4.6.0 scope, remaining doc phases, build and
tag steps, Doxygen regeneration procedure.

BACKLOG.md

@@ -0,0 +1,40 @@
+# Backlog
+
+Known issues and deferred items (code and docs). Format: `ID — item — context/status`.
+
+## Code
+
+- **AC-LEGACY** — Remove the legacy `queit` subitem alias for AC quiet mode
+  (`out_ac.cpp`, `QUIET_LEGACY_P`). Fixed the typo to `quiet` in v4.6.0; drop the alias
+  in the next major release.
+- **RGB-DEAD** — The `/RGB` topic suffix is dead: `S_RGB` is not handled by the core
+  (`item.cpp`) nor by color drivers (`colorchannel.cpp`); numeric strings in the common/`/set`
+  topic are parsed as HSV. Either implement RGB input parsing or remove `/RGB` from the
+  suffix table.
+- **HEX-RRGGBB** — Home Remote `#RRGGBB` notation does not work: `getIntFromStr`
+  (`utils.cpp`) silently skips hex characters, so `#FF0000` yields 0. Either implement
+  hex parsing in `Ctrl()` or drop the notation from docs.
+- **PID-CHAN-TYPE** — `out_pid::getChanType()` returns `CH_THERMO` (5) instead of `CH_PID` (13)
+  (`out_pid.cpp`). Verify whether this is intentional (core treats PID as a thermostat for
+  ON/OFF semantics) and document or fix.
+- **CAN-SPI** — External SPI CAN controller support for chips without built-in CAN
+  (Mega2560, ESP8266) — designed in the CAN draft doc, not implemented in `candriver.cpp`.
+- **ROTARY-T99** — Rotary input `T:99` with profiles and `goto`/`onenter` handlers
+  ("scenario" rotary encoder) — designed in the rotary draft doc, not implemented.
+- **PWM-ESP32** — PWM on ESP32 is a stub: `analogWrite` body is `//TBD`
+  (`out_pwm.cpp`). CH_PWM/RGB/RGBW/RGBWW do not work on ESP32 targets.
+- **SPILED-DMX-SUBITEM** — LED pixel addressing via subitem (10-20) works only for
+  CH_SPILED; the DMX driver ignores subitem. Clarify or implement.
+
+## Docs
+
+- **DOC-EN** — Bilingualization: port RU docs to EN (GitHub Wiki / developer site).
+  Baseline: `documentation/reference/dokuwiki-2026-10-02/` + audited RU docs.
+- **DOC-WIKI** — Sync the lazyhome.ru dokuwiki with the repo (CAN 50 kbit/s, sprinkler DRY
+  features, rotary encoder, new channel types).
+- **DOC-SITE** — lighthub.github.io: push, optional CI regeneration of Doxygen on code
+  changes.
+
+## Release v4.6.0 (see RELEASE_PLAN_v4.6.0.md)
+
+- Build all 16 targets, attach binaries, tag `v4.6.0`, release notes.