pyright-envslisted

## The problem In a monorepo where several packages each vendor their own copy of the same third-party module, a single flat Pylance/Pyright index cannot tell which copy a given file should resolve against. Picture two packages, `alpha` and `beta`, each with their own `vendor/sharedlib/` directory containing a different build of the same library. Without per-package isolation, Ctrl+click (Go to Definition) from a file in `alpha` can just as easily land in `beta`'s copy — whichever one the editor happened to index first. The bug is silent: imports still resolve, autocomplete still works, but they point at the wrong file, and refactors made through "Go to Definition" edit the wrong package. Pyright's `executionEnvironments` setting fixes this: each package gets its own `root` and its own `extraPaths`, so Pyright resolves imports for a file against that package's paths only. Hand-writing dozens of these entries for a real monorepo is not something anyone wants to do by hand, or keep in sync as packages come and go. This tool generates the whole `executionEnvironments` list from a small config file. ## How the fix works 1. Every discovered package becomes one entry: `{"root": "<package>", "extraPaths": [...]}`. 2. `extraPaths` are ordered source dirs, then vendor dirs, then shared roots, then test dirs, deduplicated. 3. A path is only emitted if it exists on disk. A configured shared root that does not exist is dropped and reported once on stderr, never silently swallow