fix: uv cannot lock a project that declares no name or version

[VXNCXNX]

What's broken

With use_uv enabled, a project that declares no project.name cannot be locked or installed. uv requires name and version, PDM allows an application to omit both, and the pyproject.toml PDM generates for uv omits them too.

Fixes #3421

Repro

A pyproject.toml with a description and dependencies but no name or version:

$ pdm lock
before:
  TOML parse error at line 1, column 1
  `pyproject.toml` is using the `[project]` table, but the required
  `project.name` field is not set
  error: Failed to parse: `pyproject.toml`

after:
  Resolved 2 packages in 2ms
  Lock successful.
$ pdm install
  Installed 1 package in 3ms
   + packaging==26.3

The fix

Write a placeholder name and version into the generated file, then filter that root entry out again when the uv lockfile is read back, so it never reaches pdm.lock. The version is only filled when it is not declared dynamic, otherwise a dynamic version would be overwritten.

Verification

Two tests, one per half of the fix. Removing the name fill fails the first, dropping the dynamic-version guard fails the second.

I ran the real commands rather than only the unit tests: pdm lock and pdm install against a real uv, and grep confirms the placeholder does not appear in the generated pdm.lock. A named project and a project with a dynamic version both still lock unchanged.

Suite: 1340 passed. Two failures, test_run_script_with_inline_metadata and test_export_from_pylock_not_empty, are identical on a clean checkout here. ruff check and ruff format --check clean on the touched files.

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[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.47%. Comparing base (29c40ea) to head (ef4c8c3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pdm/formats/uv.py	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3849      +/-   ##
==========================================
+ Coverage   88.41%   88.47%   +0.06%     
==========================================
  Files         121      121              
  Lines       13258    13270      +12     
  Branches     2252     2253       +1     
==========================================
+ Hits        11722    11741      +19     
+ Misses        966      963       -3     
+ Partials      570      566       -4     

Flag	Coverage Δ
unittests	88.36% <96.42%> (+0.06%)	⬆️

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