fix: make Ubuntu installation and CI actually runnable

[turinglambdaai]

Fixes the concrete cross-platform failures reproduced in CI, with Ubuntu as the priority.

Root causes found

1. raco pkg install --name tessera --link . is rejected by Racket 9.3 because . is not a valid ending path element for a named linked package, so CI previously never reached the real runtime tests.
2. Linux smoke tests hard-coded Retina/2x framebuffer coordinates. Ubuntu/Xvfb reports scale 1.0, which caused out-of-range pixel reads.
3. Linux CJK smoke coverage used fonts that the current pure-Racket TrueType/glyf parser cannot necessarily consume. CI now installs WenQuanYi Zen Hei and points TESSERA_FONT at its TTC.
4. macos-latest is ARM64, while the old workflow installed x64 Racket and Homebrew installed arm64 GLFW, so FFI reported GLFW as missing due to an architecture mismatch.
5. Several GLFW context-hint constants in the Racket FFI binding were incorrect. They are now aligned with glfw3.h.
6. GitHub's hosted macOS 26 ARM64 runner can load Cocoa/NSGL GLFW but does not expose a usable NSGL pixel format. Full macOS window/render smoke tests therefore cannot be truthfully validated on that hosted runner.

Changes

• install the linked package from an absolute workspace path
• add a compile gate before runtime tests
• install explicit GLFW/Mesa/Xvfb/font runtime dependencies on Ubuntu
• run the complete Ubuntu GUI/OpenGL/snapshot suite under Xvfb with software Mesa
• make pixel smoke tests use the actual framebuffer scale instead of hard-coded 2x coordinates
• run native arm64 Racket on the current arm64 macOS runner
• verify GLFW FFI loading and non-window tests on the macOS hosted runner
• prefer 4x MSAA but retry window creation without multisampling when the requested pixel format is unavailable
• allow Cocoa graphics switching/offline renderer selection on macOS
• correct GLFW context-hint constants
• add CI concurrency cancellation so superseded PR runs do not clog the queue
• update English/Chinese setup, troubleshooting and CI documentation

Validation

• Ubuntu 24.04 x64: package install, compile, GLFW/OpenGL runtime, text rendering, snapshots and full test suite pass under Xvfb + software Mesa.
• macOS 26 ARM64 hosted runner: native ARM64 Racket install, package install, compile, Homebrew GLFW FFI loading and non-window tests pass.
• Full macOS rendering remains a physical/self-hosted Mac validation responsibility because the GitHub-hosted runner has no usable NSGL pixel format.

Final CI run for head 237766319ad982d380ab3feb4b66326c32a0f1e4 is green on both matrix jobs.