Declare aiohttp server dependency for documented HTTP mode

[Justinabox]

Summary

The README documents HTTP server mode after installing .[sqlite], but aiohttp is not declared in pyproject.toml as either a default dependency or an optional server extra. In a clean environment that follows the documented dependency set, importing/running server.py fails before any modem setup.

Evidence

Docs and packaging:

• README.md:35-43 installation says pip install -e ".[sqlite]".
• README.md:68-83 then documents python server.py and HTTP endpoints.
• pyproject.toml:10-21 declares only pyserial-asyncio by default and only aiosqlite under the sqlite extra; no aiohttp / pytest-aiohttp runtime server extra exists.
• server.py:10-11 imports aiohttp / aiohttp.web at module import time.

Clean-environment repro, intentionally installing only the documented runtime pieces (pyserial-asyncio plus aiosqlite) and using PYTHONPATH=. to avoid editable-install side effects:

rm -rf /tmp/callstack-clean-env && uv venv /tmp/callstack-clean-env >/dev/null
/tmp/callstack-clean-env/bin/python -m pip install pyserial-asyncio aiosqlite >/dev/null 2>&1
PYTHONPATH=. /tmp/callstack-clean-env/bin/python - <<'PY'
try:
    import server
    print('import server: ok')
except Exception as exc:
    print(f'import server: {type(exc).__name__}: {exc}')
PY
PYTHONPATH=. /tmp/callstack-clean-env/bin/python - <<'PY'
try:
    import callstack
    from callstack import ModemConfig
    print(f'import callstack + ModemConfig: ok {ModemConfig.__name__}')
except Exception as exc:
    print(f'import callstack: {type(exc).__name__}: {exc}')
PY

Observed output:

import server: ModuleNotFoundError: No module named 'aiohttp'
import callstack + ModemConfig: ok ModemConfig

Baseline health from this scout run:

git diff --check
# exit 0

PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/ -q
# first run: 1 transient failure in tests/test_sms_service.py::test_receive_cmti
# immediate focused rerun: passed
# immediate full rerun: 314 passed in 4.22s

Duplicate checks run before filing:

gh issue list --state all --search 'aiohttp server.py optional dependency pyproject in:title,body'
gh issue list --state all --search 'HTTP server install extra aiohttp in:title,body'
gh issue list --state all --search 'server.py ModuleNotFoundError aiohttp in:title,body'
# only unrelated #22 CLI issue surfaced in one broad search

Expected behavior

A user following the documented installation path for HTTP server mode should either:

• get aiohttp installed automatically, or
• be told to install a documented optional extra such as .[server] or .[server,sqlite] before running python server.py.

Actual behavior

The documented .[sqlite] dependency set is enough for SQLite persistence but not enough for server.py; the first import server fails with ModuleNotFoundError: No module named 'aiohttp' in a clean environment.

Suggested fix direction

• Add a runtime server extra, for example:

[project.optional-dependencies]
server = [
    "aiohttp>=3.9",
]

• Consider a convenience extra such as all = ["callstack[sqlite,server]"] if setuptools metadata supports it cleanly.
• Update README HTTP Server Mode / installation snippets to use the correct extra, e.g. pip install -e ".[server,sqlite]".
• Keep test-only pytest-aiohttp under dev/test dependencies rather than server runtime dependencies.

Acceptance criteria

• pyproject.toml declares the runtime dependency needed by server.py.
• README's HTTP server instructions install that dependency.
• A clean virtualenv can run python -c "import server" after following the documented server install command.
• Existing baseline tests continue to pass.

Verification gates

git diff --check
python -m venv /tmp/callstack-server-extra-check
/tmp/callstack-server-extra-check/bin/python -m pip install -e ".[server,sqlite]"
/tmp/callstack-server-extra-check/bin/python -c "import server; print('server import ok')"
PYTHONPATH=. uv run --no-project --with pytest --with pytest-asyncio --with pytest-aiohttp --with pyserial-asyncio --with aiosqlite pytest tests/ -q