Warn on invalid uv.toml when provided via direct path (#14653)

## Summary

We validate the `uv.toml` when it's discovered automatically, but not
when provided via `--config-file`. The same limitations exist, though --
I think the lack of enforcement is just an oversight.

Closes https://github.com/astral-sh/uv/issues/14650.

crates/uv-settings/src/lib.rs

@@ -170,7 +170,12 @@ impl FilesystemOptions {
 
     /// Load a [`FilesystemOptions`] from a `uv.toml` file.
     pub fn from_file(path: impl AsRef<Path>) -> Result<Self, Error> {
-        Ok(Self(read_file(path.as_ref())?))
+        let path = path.as_ref();
+        tracing::debug!("Reading user configuration from: `{}`", path.display());
+
+        let options = read_file(path)?;
+        validate_uv_toml(path, &options)?;
+        Ok(Self(options))
     }
 }
 

crates/uv/tests/it/pip_install.rs

@@ -267,7 +267,7 @@ fn invalid_toml_filename() -> Result<()> {
 }
 
 #[test]
-fn invalid_uv_toml_option_disallowed() -> Result<()> {
+fn invalid_uv_toml_option_disallowed_automatic_discovery() -> Result<()> {
     let context = TestContext::new("3.12");
     let uv_toml = context.temp_dir.child("uv.toml");
     uv_toml.write_str(indoc! {r"
@@ -288,6 +288,30 @@ fn invalid_uv_toml_option_disallowed() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn invalid_uv_toml_option_disallowed_command_line() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let uv_toml = context.temp_dir.child("foo.toml");
+    uv_toml.write_str(indoc! {r"
+        managed = true
+    "})?;
+
+    uv_snapshot!(context.pip_install()
+        .arg("iniconfig")
+        .arg("--config-file")
+        .arg("foo.toml"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to parse: `foo.toml`. The `managed` field is not allowed in a `uv.toml` file. `managed` is only applicable in the context of a project, and should be placed in a `pyproject.toml` file instead.
+    "
+    );
+
+    Ok(())
+}
+
 #[test]
 fn cache_uv_toml_credentials() -> Result<()> {
     let context = TestContext::new("3.12");