Move CI, dev tools, and configs from root-level scattered locations into
a
unified `dev/` directory structure. Update all references across build
scripts, documentation, and editor configurations.

Also consolidate editor config generation into build.rs for automated
synchronization of rust-analyzer settings across VS Code and Zed.

Document that the dirtiness check compares content, not timestamps,
and add the `--show-diff` flag example used by CI workflows.

Update contributor and dev docs to reflect the new `mingling_ci` crate,
`ci.py` orchestration script, and subcommand-based CI workflow.

Split test-examples into two phases: build all examples in parallel
first, then run tests serially against pre-built binaries. Abort on any
build failure instead of skipping tests for that example.

Replace the centralized `examples/test-examples.toml` with individual
`test.toml` files in each example directory, updating the test runner
and related documentation accordingly.

Replace the separate code/docs CI jobs and local check flags with
a unified `--check-*` flag system, enabling each check to run
independently across a platform matrix.

Replace relative file links with absolute URLs and add centered page
headers
to the migrated docs. Update the dev sidebar to include the new pages.