Surface package install origin (editable/local/VCS) in getPackages so requirements can be reconstructed faithfully

The env-safety fix in #14328 (PR #14520) builds the pip install -r / uv pip install -r requirements file from the kernel's
installed-package list (getPackagesInstalled -> getPackages), naming every installed package so the resolver honors all constraints.
That list is name-only, so packages installed editable (-e), from a local path, or from a VCS URL are emitted as bare names.

That's correct for the common case, but bare-naming a non-PyPI package has edges when the resolver has to move it (a version conflict, or
Update All's --upgrade, which seeks a newer version of everything):

• A different package with the same name on the configured index could be substituted (name collision).
• Update All could fail with "no matching distribution" for a local-only package instead of keeping the installed copy.

Proposal

Surface install origin on LanguageRuntimePackage so package operations can emit a faithful requirement line for these packages instead of
a bare name.

• The Python kernel's _get_packages_installed already walks importlib.metadata.distributions(); it can read each dist's PEP 610
  direct_url.json to determine whether it was installed editable, from a local directory/archive, or from a VCS.
• Add a field (e.g. editable: boolean and/or source/directUrl) to LanguageRuntimePackage in positron.d.ts.
• The pip/uv package managers then emit name @ file://... / -e ... for those packages and bare names for the rest, eliminating both
  edges above.

Some of this information is not portable to other languages, so we might want to consider supporting a generic type, like Map<string, string> instead of enumerating every possible field required per language.

Notes

• Enhancement: current bare-name behavior is correct for normal PyPI packages, which is the overwhelming majority.

See #14328.

Start by tracing getPackagesInstalled through getPackages and the Python kernel’s _get_packages_installed, then inspect LanguageRuntimePackage in positron.d.ts and the pip/uv package managers. Confirm how PEP 610 direct_url.json represents editable, local, and VCS installs. Done means preserving those origins in package data and emitting faithful requirement lines while keeping ordinary packages as bare names.