Improve error message when a virtual environment Python symlink is broken (#12168)

When removing a Python interpreter underneath an existing venv, uv
currently shows a not found error:

```
error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
  Caused by: Python interpreter not found at `/home/konsti/projects/uv/.venv/bin/python3`
```

This is unintuitive, as the file for the Python interpreter does exist,
it is a broken symlink that needs to be replaced with `uv venv`.

I've been encountering those occasionally, and I expect users that
switch between versions a lot will, too, especially when they also use
pyenv or a similar Python manager.

The new error hints at this solution:

```
error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
  Caused by: Broken symlink at `.venv/bin/python3`, was the underlying Python interpreter removed?

hint: To recreate the virtual environment, run `uv venv`
```

crates/uv-python/src/interpreter.rs

@@ -677,6 +677,8 @@ impl Display for StatusCodeError {
 pub enum Error {
     #[error("Failed to query Python interpreter")]
     Io(#[from] io::Error),
+    #[error(transparent)]
+    BrokenSymlink(BrokenSymlink),
     #[error("Python interpreter not found at `{0}`")]
     NotFound(PathBuf),
     #[error("Failed to query Python interpreter at `{path}`")]
@@ -699,6 +701,33 @@ pub enum Error {
     Encode(#[from] rmp_serde::encode::Error),
 }
 
+#[derive(Debug, Error)]
+pub struct BrokenSymlink {
+    pub path: PathBuf,
+    /// Whether the interpreter path looks like a virtual environment.
+    pub venv: bool,
+}
+
+impl Display for BrokenSymlink {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "Broken symlink at `{}`, was the underlying Python interpreter removed?",
+            self.path.user_display()
+        )?;
+        if self.venv {
+            writeln!(
+                f,
+                "\n\n{}{} Consider recreating the environment (e.g., with `{}`)",
+                "hint".bold().cyan(),
+                ":".bold(),
+                "uv venv".green()
+            )?;
+        }
+        Ok(())
+    }
+}
+
 #[derive(Debug, Deserialize, Serialize)]
 #[serde(tag = "result", rename_all = "lowercase")]
 enum InterpreterInfoResult {
@@ -879,7 +908,24 @@ impl InterpreterInfo {
             .and_then(Timestamp::from_path)
             .map_err(|err| {
                 if err.kind() == io::ErrorKind::NotFound {
-                    Error::NotFound(executable.to_path_buf())
+                    // Check if it looks like a venv interpreter where the underlying Python
+                    // installation was removed.
+                    if absolute
+                        .symlink_metadata()
+                        .is_ok_and(|metadata| metadata.is_symlink())
+                    {
+                        let venv = executable
+                            .parent()
+                            .and_then(Path::parent)
+                            .map(|path| path.join("pyvenv.cfg").is_file())
+                            .unwrap_or(false);
+                        Error::BrokenSymlink(BrokenSymlink {
+                            path: executable.to_path_buf(),
+                            venv,
+                        })
+                    } else {
+                        Error::NotFound(executable.to_path_buf())
+                    }
                 } else {
                     err.into()
                 }