feat: add uvx (uv tool run) package executor (#357)

* feat(uvx): add uvx (uv tool run) package executor

Adds support for `uvx`, implemented as a PyPI Executor alongside pipx.
uvx is an alias for `uv tool run`: it installs a tool into an ephemeral
environment and runs it, so it has no install/list subcommand and the
first positional argument (or --from) is the package to audit.

Parsing highlights:
- --from overrides the positional command as the package to audit
- --with packages are audited as additional environment dependencies
- name@version shorthand (ruff@0.3.0, ruff@latest) is normalized
- flag parsing stops at the tool name so the tool's own flags are not
  misread as uvx options; uvx's value/boolean flags are registered so
  none greedily consume the package positional
- VCS/URL/local-path specs are skipped for registry auditing

Wires up command registration, analytics, shell alias/shim, cloud audit
mapping, a dedicated `uvx` sandbox profile (UV_*/PIP_* env, uv cache and
tool dirs), config policy, docs, unit tests and an E2E workflow step.

Closes #326

https://claude.ai/code/session_011hyLxq7oWJX5Dp4tCEfG19

* chore(uvx): align docs and base profile with uvx support

Incorporates the low-risk, non-parser improvements from the community
PR #345 (author non-responsive) into our implementation:

- list uvx (and the previously-missing pipx) as PyPI managers in the
  pypi-restrictive base profile package_managers and its README, so the
  base profile applies directly when selected via --sandbox-profile
- document uvx in docs/github-action.md and docs/proxy-mode.md
- add version / IsExplicitVersion assertions to the uvx parser tests

Our pflag-based parser is kept as-is: unlike #345 it audits --with
packages and handles all uvx short flags (e.g. -w), both of which the
community PR misses.

* fix(uvx): skip interpreter requests; use require in tests

Addresses review feedback on PR #357:

- uvx interpreter requests (`uvx python`, `uvx python@3.12`, `uvx pypy`,
  ...) launch an isolated interpreter rather than installing a PyPI tool.
  Treating the positional as a package made the guard flow resolve/analyze
  pkg:pypi/python (and python==3.12), which could wrongly block or fail a
  valid invocation. Skip these for the positional; --with packages on the
  same command are still audited.
- Use require.NoError / require.Len for fatal assertions in the uvx tests,
  matching the repo's testing convention, so a failure stops the subtest
  before a nil dereference instead of panicking.

* docs(uvx): document fail-open and --with-requirements trade-offs

Record the two deliberate parsing decisions raised in review as in-code
trade-off comments (no behavior change):

- unknown flags are tolerated (fail open), consistent with the other
  executors; the residual gap only affects non-proxy guard mode since the
  default proxy flow intercepts every registry download.
- --with-requirements / --with-editable values are consumed but not
  expanded into audit targets; expanding them needs manifest-extractor and
  guard changes, tracked as follow-up. Proxy mode still covers them.

* docs(uvx): drop --with-requirements limitation note

Per maintainer review: guard mode is being deprecated and auditing the
contents of an existing requirements file is a scanner's responsibility,
not PMG's. Remove the "known limitation / follow-up" note; the flags stay
registered only so their values are not mistaken for the tool positional.

---------

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/pmg-e2e.yml

@@ -83,7 +83,7 @@ jobs:
         run: |
           test -f $HOME/.pmg.rc
           test -d $HOME/.pmg/bin
-          for shim in npm pip pip3 pnpm bun uv yarn poetry npx pnpx; do
+          for shim in npm pip pip3 pnpm bun uv uvx yarn poetry npx pnpx; do
             test -x $HOME/.pmg/bin/$shim || { echo "Missing shim: $shim"; exit 1; }
           done
 
@@ -416,6 +416,33 @@ jobs:
 
           cd - && rm -rf "$PNPX_TESTDIR"
 
+      - name: Test UVX - Package Execution
+        run: |
+          echo "Testing UVX package execution (uv tool run)..."
+          UVX_TESTDIR=$(mktemp -d) && cd "$UVX_TESTDIR"
+
+          echo "Testing uvx with a simple tool in proxy mode (default)..."
+          pmg uvx ruff@0.6.9 --version | tee uvx-output.txt
+          # Verification: pinned version is resolved and executed via the proxy
+          grep -q "0.6.9" uvx-output.txt
+
+          echo "Testing uvx version pin via @ syntax (non-proxy)..."
+          pmg --proxy-mode=false uvx ruff@0.6.9 --version | tee uvx-pin-output.txt
+          grep -q "0.6.9" uvx-pin-output.txt
+
+          echo "Testing uvx with --from (command name differs from package)..."
+          pmg --proxy-mode=false uvx --from cowsay cowsay -t "Hello from pmg uvx" | tee uvx-from-output.txt
+          # Verification: cowsay output contains our message and cow art
+          grep -q "Hello from pmg uvx" uvx-from-output.txt
+          grep -q '\^__\^' uvx-from-output.txt
+
+          echo "Testing uvx dry-run mode..."
+          pmg --proxy-mode=false --dry-run uvx --from cowsay cowsay -t "This should not execute" | tee uvx-dry-output.txt
+          # Verification: dry-run should NOT produce cowsay ASCII art (cow face ^__^)
+          ! grep -q '\^__\^' uvx-dry-output.txt
+
+          cd - && rm -rf "$UVX_TESTDIR"
+
       - name: Test Pip - Single Package & Manifest
         run: |
           echo "Testing Pip single package installation..."