Put the deployment-only dependencies behind a server extra

A data-science environment installing fluksio waited for lxml, aiohttp and
the rest of a connector stack it has nothing to talk to. Outbound mail,
error reporting and the MQTT and InfluxDB clients moved to
`fluksio[server]`, which the image installs; each import is guarded and
names the extra. `tenacity` had no import site at all and is gone.

23 fewer packages and the compiled ones among them — a bare `pip install
fluksio` still serves, runs every python node, and registers the mqtt and
influxdb node types, which only need the library when one is actually
built. sentry-sdk arrives anyway underneath `fastapi[standard]`; what
changed there is that nothing of ours requires it.

The dev environment keeps every extra: the suite exercises the connectors
and strict mypy checks their call sites.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019Hra4ndWMCLU5F3KjUuVAc

backend/pyproject.toml

@@ -25,15 +25,12 @@ dependencies = [
     "fastapi[standard]<1.0.0,>=0.114.2",
     "python-multipart<1.0.0,>=0.0.7",
     "email-validator<3.0.0.0,>=2.1.0.post1",
-    "tenacity<9.0.0,>=8.2.3",
     "pydantic>2.0",
-    "emails<1.0,>=0.6",
     "jinja2<4.0.0,>=3.1.4",
     "alembic<2.0.0,>=1.12.1",
     "httpx<1.0.0,>=0.25.1",
     "sqlmodel<1.0.0,>=0.0.21",
     "pydantic-settings<3.0.0,>=2.2.1",
-    "sentry-sdk[fastapi]>=2.20.0",
     "pyjwt<3.0.0,>=2.8.0",
     "pwdlib[argon2,bcrypt]>=0.3.0",
     "numpy>=2.2.6",
@@ -43,8 +40,6 @@ dependencies = [
     # copied onto other people's machines and stays dependency-free.
     "orjson>=3.10",
     "cryptography>=44.0.0",
-    "aiomqtt>=2.0.0",
-    "influxdb-client[async]>=1.40.0",
     "croniter>=1.3.0",
     "mcp>=1.29,<2",
     "fluksio-worker>=0.1,<0.2",
@@ -62,6 +57,17 @@ dependencies = [
 # extra rather than a dependency: csv and jsonl need nothing, and pyarrow is
 # tens of megabytes for whoever wants dtypes kept.
 parquet = ["pyarrow>=17"]
+# What a deployment has and a laptop does not: the device connectors, outbound
+# mail and error reporting. The engine, the CLI and every python node work
+# without them — `pip install fluksio` in a data-science environment is the
+# case this exists for, and lxml and the aiohttp stack are most of its wait.
+# Each import is guarded and names this extra. The image installs it.
+server = [
+    "emails<1.0,>=0.6",
+    "sentry-sdk[fastapi]>=2.20.0",
+    "aiomqtt>=2.0.0",
+    "influxdb-client[async]>=1.40.0",
+]
 
 [project.urls]
 Homepage = "https://fluksio.com"