feat: render the panel image as a 1-bit 800x480 BMP or PNG

With the move to BYOS there is no TRMNL cloud to interpret a Liquid
template, so the application draws the screen itself.

The pipeline is satori (flexbox to SVG) then resvg (SVG to pixels) then
a hand-written 1-bit encoder. Chromium was the alternative and was
rejected: half a gigabyte and a real memory appetite in the runtime
image, for a screen of eight blocks. Playwright still handles the E2E
tests, in its own pinned image, never in the application one.

The payoff is testability. The layout is asserted on the element tree
and the geometry on the SVG text, so a rendering regression shows up as
a readable diff instead of a pixel comparison. The BMP and PNG encoders
are verified field by field against their specifications, including an
independent CRC-32 for the PNG: a device rejecting a malformed image is
expensive to debug from a shop window.

Two properties are pinned because the battery depends on them: the same
payload must produce byte-identical output, and changed hours must
produce different output. The filename handed to the device is a hash of
these bytes, and the firmware skips the redraw when it is unchanged.

The fonts are vendored into public/fonts and the logo into public/brand,
both committed. Rendering must not depend on an install tree, a CDN or
the network, or the bytes drift and the panel wakes for nothing.

`npm run screen:preview` writes a real 1-bit image plus a magnified view,
which is where clipping and thin strokes give themselves up. That is how
the week strip was caught clipping and condensed.

`npm run brand` rebuilds the assets: it locates the wordmark band in the
shop logo rather than hard-coding offsets a future revision would break,
and thresholds it with the panel's own encoder. sharp is a devDependency
used only there; nothing at runtime needs it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012cSY9pVhZmJUKNN7wf1Myd

lib/screen/layout.ts

@@ -0,0 +1,24 @@
+/**
+ * Screen geometry and typography, in one place.
+ *
+ * The panel is 800x480 and strictly 1-bit: there is no grey to lean on, so
+ * hierarchy has to come from size, weight and solid inversion. Nothing here
+ * may introduce a shadow, a gradient or a hairline — they dither into mud on
+ * e-ink and cost a redraw for nothing.
+ */
+
+export const SCREEN_WIDTH = 800;
+export const SCREEN_HEIGHT = 480;
+
+export const BLACK = '#000000';
+export const WHITE = '#ffffff';
+
+export const PADDING = 24;
+export const HEADER_HEIGHT = 76;
+export const WEEK_HEIGHT = 112;
+export const BANNER_HEIGHT = 84;
+/** Solid rules only; anything thinner than 2px breaks up on e-ink. */
+export const RULE = 3;
+
+export const SANS = 'Inter';
+export const SERIF = 'Source Serif 4';