fix(web): accept every panel size and row address type the rgbmatrix library does

The Display form capped columns at 128 and chain length at 24, and its
submit handler (fixInvalidNumberInputs) rewrote anything larger to the cap,
so wide panels and long chains silently saved as the wrong size. The config
API checked none of the hardware numbers, so values the library rejects (odd
rows, parallel 4, PWM dither bits 3) saved and the matrix then refused to
start.

- Form limits now match the pinned library: rows even 8-64, cols >= 16 and
  chain_length >= 1 with no upper bound, parallel 1-3, PWM dither bits 0-2,
  PWM LSB nanoseconds 50-3000.
- save_main_config rejects out-of-range rows, cols, chain_length, parallel,
  brightness, scan_mode, pwm_bits, pwm_dither_bits, pwm_lsb_nanoseconds and
  gpio_slowdown with a 400.
- A stored gpio_slowdown or pwm_dither_bits of 0 renders as 0 instead of the
  default, so saving the tab no longer overwrites it.
- Row Address Type offers 5 (SM5368 / B707 row shift register). Verified on a
  Waveshare 96x48 V2 (24S-A1) on a Pi 4 with the Adafruit Triple LED Matrix
  Bonnet: rows 48, cols 96, row address type 5, BGR, GPIO slowdown 8.
- Help text and docs: FM6124-family panels use Panel Type Standard; on a Pi 5
  the library supports only row address types 0 and 2.

No change to the rpi-rgb-led-matrix submodule.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -494,15 +494,18 @@ These settings control the physical hardware configuration and how the matrix is
 - **`rows`** (integer, default: 32)
   - Number of LED rows (vertical pixels) in each panel
   - Common values: 16, 32, 48, 64
+  - Must be an even number from 8 to 64 (the rgbmatrix library's limit)
   - Must match your physical panel configuration
 
 - **`cols`** (integer, default: 64)
   - Number of LED columns (horizontal pixels) in each panel
   - Common values: 32, 64, 96, 128
+  - At least 16, with no upper limit
   - Must match your physical panel configuration
 
 - **`chain_length`** (integer, default: 2)
   - Number of LED panels chained together horizontally
+  - At least 1, with no upper limit; longer chains lower the refresh rate
   - If you have 2 panels side-by-side, set to 2
   - If you have 4 panels in a row, set to 4
   - Total display width = `cols × chain_length`
@@ -511,13 +514,14 @@ These settings control the physical hardware configuration and how the matrix is
   - Number of parallel chains (panels stacked vertically)
   - Use 1 for a single row of panels
   - Use 2 if you have panels stacked in two rows
+  - 1–3 on a Raspberry Pi, and the HAT needs that many outputs
   - Total display height = `rows × parallel`
 
 #### Brightness and Visual Settings
 
-- **`brightness`** (integer, 0-100, default: 90)
+- **`brightness`** (integer, 1-100, default: 90)
   - Display brightness level
-  - Lower values (0-50) are dimmer, higher values (50-100) are brighter
+  - Lower values (1-50) are dimmer, higher values (50-100) are brighter
   - Recommended: 70-90 for indoor use, 90-100 for bright environments
   - Very high brightness may cause distortion or require more power
 
@@ -612,7 +616,18 @@ These settings are typically only needed for non-standard panels or custom confi
 - **`row_address_type`** (integer, default: 0)
   - How rows are addressed on the panel
   - Most panels use 0 (direct addressing)
-  - Some panels require 1 (AB addressing) or 2 (ABC addressing)
+  - 1 = AB-addressed, 2 = direct row select, 3 = ABC-addressed,
+    4 = ABC shift + DE direct (SM5266), 5 = SM5368 / B707 row shift register
+  - ABC panels (no E line, e.g. many 128x64 FM6124 panels) use 3
+  - Panels with SM5368 row drivers use 5 with `led_rgb_sequence` `"BGR"` —
+    e.g. the Waveshare 96x48 V2 (back silkscreen `24S-A1`; the V1, `24S-A2.1`,
+    uses the defaults). This is what Waveshare's `96X48_1_24_SM5368` panel
+    type sets in their library fork.
+  - SM5368 row drivers are timing-sensitive: if rows jump up and down or the
+    bottom row shows a copy of other rows, raise `gpio_slowdown`. On a Pi 4
+    with an Adafruit Triple LED Matrix Bonnet, 4 left rows jumping; 6–8 gave a
+    stable image.
+  - On a Raspberry Pi 5 the rgbmatrix library currently supports only 0 and 2
   - Check your panel datasheet if display appears corrupted
 
 - **`multiplexing`** (integer, default: 0)
@@ -632,6 +647,8 @@ These settings control runtime behavior and GPIO timing:
   - **Raspberry Pi 4**: Use 4
   - **Raspberry Pi 5**: Use 1–2 in PIO mode (`rp1_rio: 0`, the default); start with `1` and increase if you see flickering
   - **Raspberry Pi Zero/1**: Use 1-2
+  - Range: 0-10. Panels on `row_address_type` 5 (SM5368 row drivers) can need
+    6-8 on a Pi 4
   - Incorrect values can cause display corruption, flickering, or system instability
   - If you experience issues, try adjusting this value up or down by 1