Send the screenshot to the multimodal model inline as a base64 data URL
so summarisation no longer requires S3 to be configured or publicly
reachable. Only when the PNG exceeds the provider MaxInlineBytes limit
do we upload to S3, verify the public URL is reachable, and delete the
temporary object once done. Oversized images without S3 now surface a
clear hint instead of a hard S3 requirement.
The `!darwin` guard on the modifier helpers was too broad: golang.design/x/
hotkey only exposes its Mod*/Key* constants from the darwin&&cgo, linux&&cgo
and windows backends, while the `!windows && !cgo` complement (e.g. Linux
cross-builds with CGO_ENABLED=0) falls back to a stub with no constants. That
made hk.ModCtrl/ModShift/KeyA... undefined and produced editor/vet warnings.
Realign the build tags with the upstream matrix and confine every hk.* constant
to a tagged file so the shared hotkey.go compiles everywhere. Also fix the
Linux mapping (option -> hk.Mod1; hk.ModAlt does not exist on X11).
mamamiyear