Phase 4 LVGL UI + guest channel + brand-agnostic naming

- LVGL 8.3 round-screen UI (replaces the LovyanGFX direct-draw functional UI):
  master volume arc, per-channel connection dots, SPEAKERS list, per-channel
  DETAIL (volume arc + delay -/+ + scan), SCAN list. Rendered through LovyanGFX;
  configured via build flags (LV_CONF_SKIP); tick via lv_tick_inc in loop.
- Third channel "Guest" @ I2C 0x12 (the onboard-antenna ESP32 — the long-range
  link to an occasional passenger speaker). New [env:source_guest].
- Channels are now brand-agnostic, in order: index0 "Headset" (0x11),
  index1 "Speaker 1" (0x10), index2 "Guest" (0x12). Discovery picks the real
  device per channel, so labels stay generic.
- hub_proto.h: HUB_I2C_ADDR_GUEST 0x12.

Built clean: hub_s3 (LVGL, 3 channels) + source_guest. LVGL render verified on
hardware (basic); guest board needs flashing + wiring into the I2S/I2C buses.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

platformio.ini

@@ -38,6 +38,13 @@ build_flags = '-DTARGET_SPEAKER="JBL Charge 5"' -DHUB_I2C_ADDR=0x10
 build_src_filter = +<board_source.cpp>
 build_flags = '-DTARGET_SPEAKER="Tangerine EDGE"' -DHUB_I2C_ADDR=0x11
 
+; --- Board D: I2S slave -> A2DP source -> GUEST speaker (antenna board) -------
+;     Occasional passenger speaker, furthest away (hence the onboard antenna).
+;     No hardcoded name — pick the speaker via the hub's scan UI (Phase 3).
+[env:source_guest]
+build_src_filter = +<board_source.cpp>
+build_flags = '-DTARGET_SPEAKER="Guest"' -DHUB_I2C_ADDR=0x12
+
 ; --- Hub: ESP32-S3-Touch-LCD-1.28 (round GC9A01 LCD + CST816S touch) ----------
 ;     Different chip (esp32s3) from the relay boards. Drives the UI; later the
 ;     wired control bus to Boards B/C. NOT in default_envs — build with -e hub_s3.
@@ -49,4 +56,22 @@ board_upload.flash_size = 4MB
 board_build.partitions = default.csv
 monitor_speed = 115200
 build_src_filter = +<hub_s3.cpp>
-lib_deps = lovyan03/LovyanGFX@^1.1.16
+lib_deps =
+    lovyan03/LovyanGFX@^1.1.16
+    lvgl/lvgl@^8.3.11
+; LVGL configured via build flags (LV_CONF_SKIP -> defaults + overrides), so
+; there is no separate lv_conf.h to maintain. 16-bit colour, byte-swapped for
+; the SPI panel; millis() tick; the big Montserrat fonts for glanceable text.
+; NOTE: keep flag values free of shell-special chars (parens/spaces) — they go
+; through a shell. LV_MEM_SIZE as a plain int; tick driven via lv_tick_inc() in
+; loop() (no LV_TICK_CUSTOM, which needs a parenthesised millis() expr).
+build_flags =
+    -DLV_CONF_SKIP=1
+    -DLV_COLOR_DEPTH=16
+    -DLV_COLOR_16_SWAP=1
+    -DLV_MEM_SIZE=49152
+    -DLV_FONT_MONTSERRAT_14=1
+    -DLV_FONT_MONTSERRAT_20=1
+    -DLV_FONT_MONTSERRAT_28=1
+    -DLV_FONT_MONTSERRAT_48=1
+    -DLV_USE_LOG=0

src/hub_proto.h

@@ -12,6 +12,7 @@
 
 #define HUB_I2C_ADDR_JBL    0x10
 #define HUB_I2C_ADDR_CARDO  0x11
+#define HUB_I2C_ADDR_GUEST  0x12   // antenna board: source for an occasional guest speaker
 
 // Master -> slave WRITE: first byte = command, then args (little-endian).
 #define HUB_CMD_SET_DELAY   0x01   // arg: uint16 delay_ms (0..HUB_MAX_DELAY_MS)