feat: add optional llm extra with OpenRouter client

[m-messer]

New in2lambda.llm package behind a Poetry llm extra (pip install 'in2lambda[llm]' → openai, python-dotenv, pydantic):

• client.get_client() returns an openai.OpenAI pointed at https://openrouter.ai/api/v1, keyed by $OPENROUTER_API_KEY (loaded from a .env file if present). Clear RuntimeError when the extra is missing or the key is unset.
• client.resolve_model() picks the model slug: --model value, else $IN2LAMBDA_MODEL, else DEFAULT_MODEL (openai/gpt-4o-mini).

The package imports cleanly without the extra (openai/dotenv guarded), so --doctest-modules still works on a bare install. CI now installs --all-extras. Tests are fully offline.

openai floor is ^1.55 — older releases resolve against a too-new httpx and break with a proxies TypeError.

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Stack: cli-group ← llm-client ← mathpix ← wizard-command
Base: cli-group — #24.

🤖 Generated with Claude Code

[peterbjohnson]

One real bug here, in .env handling.

get_client() calls load_dotenv() from inside the library (client.py:66). python-dotenv looks for the file by walking up from the calling module's directory, so once in2lambda is installed normally, it searches inside site-packages and never sees the user's .env. It only appears to work in a development checkout, where the package happens to sit under the project folder.

Minimal reproduction, with a library in one folder and a project in another:

project/.env            -> DEMO_KEY=from_project_dotenv
project/run_app.py      -> from libpkg import get_key; print(get_key())
site_packages/libpkg/   -> calls load_dotenv() then os.getenv("DEMO_KEY")

$ cd project && PYTHONPATH=../site_packages python3 run_app.py
key seen by library: None

find_dotenv(usecwd=True) finds it; the default doesn't. (It's easy to convince yourself otherwise from a REPL or python -c, where python-dotenv falls back to the working directory.)

This matters because the wizard docs in the next PR tell people a .env in the working directory is picked up automatically, which is exactly the case that fails.

Suggestions: load the .env once in the CLI entry point with usecwd=True, or drop python-dotenv and let click read the key via envvar=. Loading it from library code also changes the whole process's environment, which is a bit surprising for anyone importing in2lambda as a library.

Smaller points: resolve_model() duplicates what click's envvar=/default= already do on the --model option, and openai = "^1.55" caps us below openai 2.x, which will bite anyone combining in2lambda with a newer openai.