`dvc.api.get_url()` throws error when working directory is a subdirectory of repo path

Bug Report

Description

dvc.api.get_url() throws an error when the current working path is a subdirectory inside the dvc repository.

Reproduce

cat > setup.sh << EOF
mkdir -p test_repo
cd test_repo
dvc init --no-scm

mkdir -p /tmp/dvc_remote/
dvc remote add -d storage_name /tmp/dvc_remote/

echo foo > bar.txt
dvc add bar.txt
dvc push bar.txt

mkdir subdir/
EOF

cat > test.py << EOF
import os
from pathlib import Path

from dvc import api

path = "bar.txt"
os.chdir("./test_repo")
repo = os.getcwd()

print("From CWD -> repo root:")
print(f"\t{api.get_url(path=path, repo=repo)}")

os.chdir(Path(repo) / "..")
print("From CWD -> outside repo:")
print(f"\t{api.get_url(path=path, repo=repo)}")

os.chdir(Path(repo) / "subdir")
print("From CWD -> subdir in repo:")
print(f"\t{api.get_url(path=path, repo=repo)}")
EOF

sh setup.sh

python test.py

Expected

I was expecting python test.py file to output the following lines:

From CWD -> repo root:
        /tmp/dvc_remote/files/md5/d3/b07384d113edec49eaa6238ad5ff00
From CWD -> outside repo:
        /tmp/dvc_remote/files/md5/d3/b07384d113edec49eaa6238ad5ff00
From CWD -> subdir in repo:
        /tmp/dvc_remote/files/md5/d3/b07384d113edec49eaa6238ad5ff00

However, only the first two instances were true; the third one (from a subdir in repo) failed:

From CWD -> subdir in repo:
Traceback (most recent call last):
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/dvc/repo/__init__.py", line 401, in get_data_index_entry
    return index, index[key]
                  ~~~~~^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/dvc_data/index/index.py", line 838, in __getitem__
    return self._trie[key]
           ~~~~~~~~~~^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/sqltrie/serialized.py", line 58, in __getitem__
    raw = self._trie[key]
          ~~~~~~~~~~^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/sqltrie/sqlite/sqlite.py", line 266, in __getitem__
    row = self._get_node(key)
          ^^^^^^^^^^^^^^^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/sqltrie/sqlite/sqlite.py", line 204, in _get_node
    raise KeyError(key)
KeyError: ('subdir', 'bar.txt')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/rgoya/test/test.py", line 19, in <module>
    print(f"\t{api.get_url(path=path, repo=repo)}")
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/dvc/api/data.py", line 84, in get_url
    index, entry = _repo.get_data_index_entry(path)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rgoya/.pixi/envs/default/lib/python3.11/site-packages/dvc/repo/__init__.py", line 403, in get_data_index_entry
    raise OutputNotFoundError(path, self) from exc
dvc.exceptions.OutputNotFoundError: Unable to find DVC file with output 'bar.txt'

Environment information

DVC version: 3.67.1 (conda)
---------------------------
Platform: Python 3.11.13 on macOS-26.4-x86_64-i386-64bit
Subprojects:
        dvc_data = 3.18.2
        dvc_objects = 5.2.0
        dvc_render = 1.0.2
        dvc_task = 0.40.2
        scmrepo = 3.5.2
Supports:
        gdrive (pydrive2 = 1.21.3),
        http (aiohttp = 3.9.5, aiohttp-retry = 2.9.1),
        https (aiohttp = 3.9.5, aiohttp-retry = 2.9.1),
        s3 (s3fs = 2025.3.2, boto3 = 1.37.3),
        ssh (sshfs = 2025.2.0)
Config:
        Global: /Users/rgoya/Library/Application Support/dvc
        System: /Library/Application Support/dvc

Start at dvc/api/data.py in get_url and dvc/repo/init.py in get_data_index_entry, then reproduce the failure with the working directory set to the repository subdirectory. Trace how the requested path is resolved and add coverage showing that get_url returns the same remote URL from the repository root, outside the repository, and its subdirectory.