* Redesign the shared header and embed the GitHub logo as an image
Rework the shared gh-stack header (used by `view` and `modify`, and reused
by `submit` later in this stack) for a cleaner, more responsive look, and
replace the braille/ASCII Invertocat with a real image of the GitHub mark.
- Logo: embed the Invertocat PNG with go:embed and draw it via an inline-
image protocol (kitty or iTerm2). It is image-or-nothing: when no protocol
is available, stdout is not a TTY, or we are inside tmux/screen, no logo is
drawn and the text falls back to the normal left padding. Detection is
environment-based and cached so it never blocks the TUI, and a fixed kitty
image id lets the header clear or replace the logo in place instead of
leaving copies behind.
- Layout: place the logo in the top-left corner beside the title and version,
with the stack-info lines left-aligned beneath it on the same left margin.
Size the box to its content for each view so there is no trailing empty row.
- Responsiveness: hide the logo progressively — first when the viewport is too
narrow, then a little before the rest of the header at short heights, where
a vertical resize could otherwise leave a ghost of the inline image.
- Add unit tests for the header's responsive thresholds.
* Drop the unused HeaderHeight constant and dedupe the header config build
Follow-up to review feedback on the shared-header redesign:
- Remove the HeaderHeight constant. Nothing referenced it (callers compute
height via HeaderHeightFor), and its doc described a "maximum" that
HeaderHeightFor does not actually enforce, so the comment was misleading.
- In the view and modify View() methods, build the header config once and reuse
it for both RenderHeader and the height reservation instead of rebuilding it
twice per frame. The click/scroll handlers keep deriving the height from the
same config, so the header's dimensions remain a single source of truth.
Sameen Karim