docs(ssd1306): a datasheet per variant, each with its own pinout

Both SSD1306 modules are real parts and both belong in the catalogue -
the mismatch was in the docs, not the parts:
 - the 8-pin Adafruit breakout was served a datasheet listing a 4-pin
   I2C pinout (VCC/GND/SCL/SDA) that is not its header at all; it now
   documents its own 9-way pinout with the I2C and SPI role of each pin;
 - the 4-pin I2C module had NO datasheet, because docs resolve by
   component id and ssd1306-i2c-4pin.md did not exist - so the part
   showed nothing. It has one now.
Each points at the other so it is obvious which one you want.

frontend/src/components/component-docs/displays/ssd1306-i2c-4pin.md

@@ -0,0 +1,22 @@
+---
+brand: Solomon Systech
+buy: https://www.amazon.com/s?k=SSD1306+128x64+OLED+I2C+4+pin
+---
+SSD1306 monochrome OLED (128×64) on the **4-pin I²C module** — the cheap
+0.96" board most people have. The glass panel is bonded onto the PCB, so the
+part is a single piece: no separate display to wire.
+
+| Pin | Role |
+| --- | --- |
+| GND | ground |
+| VCC | 3.3–5 V |
+| SCL | I²C clock |
+| SDA | I²C data |
+
+- Default I²C address **0x3C** (some boards are 0x3D — check the silk).
+- 128×64 pixels, ~1 KB framebuffer, self-emitting: no backlight, so an unlit
+  pixel is truly off.
+- Drive it with Adafruit_SSD1306 (`&Wire`, reset `-1`) or U8g2.
+
+**Tip:** need the SPI pins, or a reset line? Use the 8-pin **SSD1306 OLED
+(Adafruit breakout)** part instead — same controller, more pins broken out.

frontend/src/components/component-docs/displays/ssd1306.md

@@ -2,17 +2,26 @@
 brand: Solomon Systech
 buy: https://www.amazon.com/s?k=SSD1306+128x64+OLED+display
 ---
-SSD1306 monochrome OLED (128×64). Talks **I²C or SPI** — pick with the
+SSD1306 monochrome OLED (128×64) on the **Adafruit-style breakout**, which
-`protocol` property. Drive it with Adafruit_SSD1306 or U8g2.
+brings the controller's full pinout out to a 9-way header. Talks **I²C or
+SPI** — pick with the `protocol` property. Drive it with Adafruit_SSD1306 or
+U8g2.
 
-| Pin (I²C) | Role |
+| Pin | I²C role | SPI role |
-| --- | --- |
+| --- | --- | --- |
-| VCC | 3.3–5 V |
+| Vin | 3.3–5 V | 3.3–5 V |
-| GND | ground |
+| 3v3 | 3.3 V regulator output | 3.3 V regulator output |
-| SCL | I²C clock |
+| Gnd | ground | ground |
-| SDA | I²C data |
+| Data | SDA (data) | MOSI |
+| Clk | SCL (clock) | SCK |
+| SA0 | address select (0x3C / 0x3D) | — |
+| DC | — | data/command |
+| CS | — | chip select |
+| Rst | reset (optional) | reset (optional) |
 
 - Default I²C address **0x3C**.
 - 128×64 pixels, ~1 KB framebuffer, self-emitting (no backlight).
 
-**Tip:** switch `protocol` to `spi` to expose the SCK / MOSI / DC / CS / RES pins.
+**Tip:** switch `protocol` to `spi` to drive it over SPI. If you only need
+I²C and want the plain 4-wire module, use the **SSD1306 OLED (I2C, 4-pin)**
+part instead.