docs(hardware): switch display to GDEY0579T93 with DESPI-c579

Strip-aspect 5.79" panel (792×272) replaces the page-shaped 7.5" choice.
Reflows the v0.1 screen layout, framebuffer memory budget, and spike 2
acceptance to validate the SSD1683-class controller path or fall back to
a ~300 LoC custom embedded-hal driver.

docs/v0.1-mvp-technical.md

@@ -73,8 +73,11 @@ We do **not** try to build the whole stack and turn it on. Each spike below
 is a small program that proves one risk before we commit to the next layer.
 
 1. **Spike 1 — Blink.** Confirm toolchain, flash, and basic GPIO.
-2. **Spike 2 — EPD.** Drive the 7.5" panel with `epd-waveshare`; full refresh
-   "hello world." Validates SPI wiring, panel timings.
+2. **Spike 2 — EPD.** Drive the GDEY0579T93 (via DESPI-c579 breakout) over
+   SPI; full refresh "hello world." Validates SPI wiring, panel timings, and
+   — critically — whether `epd-waveshare` already supports the panel's
+   controller (SSD1683-class) or whether we write a thin custom driver
+   against `embedded-hal`. Either way, ~300 LoC; this spike answers which.
 3. **Spike 3 — SD.** Mount FAT, read/write a file. Validates SPI sharing with
    EPD (or separate bus if needed).
 4. **Spike 4 — USB host.** Enumerate the Nuphy as a boot-protocol HID
@@ -173,7 +176,7 @@ ESP32-S3-N16R8: 512 KB SRAM + 8 MB PSRAM. We budget conservatively.
 |---|---|---|
 | Internal SRAM | ~120 KB | task stacks, DMA buffers, hot code paths |
 | Internal SRAM | ~80 KB | mbedtls runtime (TLS handshake working set) |
-| PSRAM | ~256 KB | EPD framebuffer (800×480×1 = 48 KB) + shadow + glyph cache |
+| PSRAM | ~128 KB | EPD framebuffer (792×272×1 ≈ 27 KB) + shadow + glyph cache |
 | PSRAM | ~512 KB | rope buffer + edit history headroom |
 | PSRAM | ~1.5 MB | gitoxide working set during push (pack delta, etc.) |
 | PSRAM | rest | heap headroom |