`_install_dependencies` (hermes memory setup) hard-aborted with
"uv not found — cannot install dependencies" whenever `uv` was not on
PATH, even when a perfectly good `pip` was available. Slim container
images and some CI environments don't ship uv, so memory-provider
dependency installation dead-ended there for no good reason.
Now: use `uv pip install` when uv is present, otherwise fall back to
`<python> -m pip install` when pip3/pip is available, and only abort
(with the uv install hint) when neither is found. The "Run manually:"
hints reflect whichever installer was selected.
Salvages #5954 by @MustafaKara7. Their patch added redundant local
`import subprocess` / `import sys` (both are already in scope — module
-level `sys`, function-top `subprocess`); this salvage drops those and
adds a regression test (TestInstallDependenciesRunner) covering all
three paths (uv / pip-fallback / abort). Verified adversarially: the
pip-fallback test fails against origin/main's unfixed code with the
exact dead-end symptom and passes with the fix.
Closes#5954.
Co-authored-by: MustafaKara7 <186085093+MustafaKara7@users.noreply.github.com>
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