/v1/tokenize returns a flat list when the text array holds a single string #4664

Describe the bug

The shape of the /v1/tokenize response follows the number of strings in the request instead of the
form of the request. src/tokenize/tokenize_parser.cpp nests the tokens only when the tokenizer
output has more than one row (outputShape[0] > 1), and a one-element array produces one row, the
same as a plain string:

{"text": "hello world"}              ->  {"tokens":[14990,1879]}
{"text": ["hello world"]}           ->  {"tokens":[14990,1879]}
{"text": ["hello world", "hi"]}     ->  {"tokens":[[14990,1879],[6023]]}

A client that sends a list and reads tokens[i] for each input gets a list of token lists for
two or more inputs, but a flat list of integers for exactly one. Batches that happen to contain one
string need special handling on the client.

None of the tests send a one-element array: the list cases in tokenize_parser_test.cpp and
tokenize_endpoint_test.cpp all use two or more strings. The docs show only the single-string
response.

To Reproduce

curl http://localhost:8000/v1/tokenize -H "Content-Type: application/json" \
  -d '{"model": "Qwen/Qwen3-8B", "text": ["hello world"]}'

Reproduced with the parser and a real Qwen3 tokenizer, following the same sequence as
src/llm/servable.cpp: parse the request, encode, build the response.

Expected behavior

An array of strings always gives a list of token lists, including an array with one string.

Note that this changes the response for clients that currently send a one-element array and rely on
the flat list.

Logs

None.

Configuration

1. OVMS version: main @ eec7daa
2. any servable that serves /v1/tokenize (LLM, VLM, embeddings, rerank)
3. N/A
4. N/A
5. N/A

Additional context

I have a patch with tests and docs and will open a PR.