chore: extract quadraui + kubeui to standalone repo

[JDonaghy]

Summary

Step 5 of the Session 346 course correction. Moves quadraui (the UI primitive library) and the kubeui demo crates out of the vimcode workspace into a standalone repo at https://github.com/JDonaghy/quadraui.

This forces the vimcode↔quadraui boundary to be enforced structurally by cargo build instead of by discipline. Per the new contract from PLAN.md: "vimcode developers/agents trust quadraui blindly via versioned crate dep" — quadraui has its own CLAUDE.md, its own tests, and its own CI.

What moved out of vimcode

• quadraui/ → new repo's quadraui/ (the library)
• kubeui-core/ → new repo's kubeui-core/
• kubeui/ → new repo's kubeui/ (TUI Kubernetes dashboard demo)
• kubeui-gtk/ → new repo's kubeui-gtk/ (GTK4 dashboard demo)
• docs/NATIVE_GUI_LESSONS.md → new repo's quadraui/docs/NATIVE_GUI_LESSONS.md

History was preserved via git subtree split for each of the 4 directories. The new repo's commit history starts from a workspace-skeleton commit and merges the four subtrees, so the line-by-line history of every quadraui/kubeui file is intact and walkable from the new repo.

What changed in vimcode

• Cargo.toml: dropped [workspace] members = [...] (vimcode is now a single-crate package again). Quadraui dep is now path = "../quadraui/quadraui" (sibling checkout); local-dev-only.
• Cargo.lock: regenerated against the extracted quadraui (now version 0.0.1).
• CLAUDE.md / PLAN.md: doc references to quadraui/docs/* now point at the new repo's URLs. Historical references to source paths (quadraui/src/...) are kept as context.
• CI temporarily disabled (commit 3abd5ec): GitHub Actions workflows can't resolve the path-dep without a sibling checkout. Renamed .yml → .yml.disabled until we decide on the sibling-clone approach (workflow step that clones quadraui first) or a git-dep with pinned rev. Local builds and tests are unaffected.

Test plan

• cargo build --no-default-features clean (vimcode side)
• cargo clippy --no-default-features -- -D warnings clean
• cargo fmt --check clean
• cargo test --no-default-features (1950 lib + integration tests) green
• Quadraui side, separately: the new repo's cargo build / test --features tui --workspace --exclude kubeui-gtk / clippy / fmt all green; 302 quadraui tests pass standalone. See https://github.com/JDonaghy/quadraui

Follow-ups (not blocking this PR)

• Re-enable vimcode CI with either a sibling-clone step or a git-dep on quadraui (pinned rev). Decide based on which DX wins for the cadence of quadraui ↔ vimcode iteration.
• Regenerate flatpak/cargo-sources.json before next vimcode release (Cargo.lock changed).
• PLAN.md historical references to quadraui/src/... paths: kept as-is; they're context for past work and would bloat this diff if rewritten. Future passes can clean up incrementally.

Diff size disclosure

~37k line deletions in vimcode are the four directories moving out — no logic was rewritten, no functions changed signatures, no behaviour shifted. Reviewers should focus on:

• Cargo.toml — workspace dropped; quadraui dep updated
• CLAUDE.md / PLAN.md — doc reference updates
• .github/workflows/ — disabled workflows

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