feat: initial ispconfig-py SDK (sites / dns / mail / databases / clients)

Python 3.10+ SDK wrapping the ISPConfig remote SOAP API so we stop writing
throwaway PHP snippets every time we need to touch a site, zone, or mailbox.

Why no zeep: ISPConfig's /remote/index.php exposes PHP SoapServer in non-WSDL
mode and refuses WSDL generation (?wsdl returns a fault). zeep requires WSDL,
so the stated dependency wouldn't actually work. Instead we hand-roll SOAP
envelopes with the stdlib (urllib + xml.etree). Zero runtime deps.

Structure:
- src/ispconfig/_soap.py        — envelope encode/decode, fault surfacing
- src/ispconfig/client.py       — ISPConfigClient context manager, retry
- src/ispconfig/exceptions.py   — ISPConfigError / Auth / Permission / NotFound / Fault
- src/ispconfig/sites.py        — web_domain get/add/update/delete + enable_php / enable_letsencrypt helpers
- src/ispconfig/dns.py          — zones + A/CNAME/MX/TXT records, dns_a_add type-column workaround
- src/ispconfig/mail.py         — mail domains, users, forwards, create_mailbox helper
- src/ispconfig/databases.py    — convenience facade over sites_database_*
- src/ispconfig/clients.py      — client + sys_groupid lookups
- src/ispconfig/types.py        — TypedDicts for response shapes (no pydantic)

Institutional knowledge baked into docstrings + README footgun list:
- sites_web_domain_update 2nd arg is client_id (not primary_id); admin = 0
- sys_groupid=1 -> pass client_id=0 on update, else ownership churns
- fastcgi_php_version vs server_php_id depending on panel version
- dns_a_add type-column bug (<= 3.2.11) — wrapper issues follow-up update
- dns_zone_get_id wants origin WITHOUT trailing dot on 3.2.11+ (contrary to
  what the older snippets say). Verified live against Rackham 2026-04-22.
- mail_user_get returns a bare map on exactly-one-match filter dicts —
  wrapper normalizes to list
- session timeouts mid-op: client detects + re-auths once (max_retries knob)

Tests:
- tests/test_unit.py   — 12 unit tests against a fake transport
- tests/test_smoke.py  — live read-only smoke test, gated on env vars:
    ISPCONFIG_TEST_URL, ISPCONFIG_TEST_USER, ISPCONFIG_TEST_PASS
  Covers login, web_domain_get(156), dns_zone_get_id, mail_user_get filter.

Tooling:
- mypy strict-ish (disallow untyped defs, warn-return-any, no implicit optional)
- ruff with E/F/W/I/B/UP/N/SLF/RUF lint sets
- pip install -e .[dev] for pytest / mypy / ruff

tests/test_smoke.py

@@ -0,0 +1,47 @@
+"""Live read-only smoke test against a real ISPConfig panel.
+
+Gated on env vars: ``ISPCONFIG_TEST_URL``, ``ISPCONFIG_TEST_USER``,
+``ISPCONFIG_TEST_PASS``. These tests are skipped if any is unset.
+
+They are **read-only** — no ``_add`` / ``_update`` / ``_delete`` calls. Safe
+to run against production.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from ispconfig import ISPConfigClient
+
+
+@pytest.fixture()
+def client(live_creds: dict[str, str]) -> ISPConfigClient:
+    with ISPConfigClient(live_creds["url"], live_creds["user"], live_creds["password"]) as c:
+        yield c  # type: ignore[misc]
+
+
+def test_login_returns_session(live_creds: dict[str, str]) -> None:
+    c = ISPConfigClient(live_creds["url"], live_creds["user"], live_creds["password"])
+    c.login()
+    assert c.session_id and len(c.session_id) > 10
+    assert c.logout() is True
+
+
+def test_get_domain_156(client: ISPConfigClient) -> None:
+    site = client.sites.web_domain_get(156)
+    assert site["domain"] == "mcbindustrial.com"
+    assert site["php"] == "fast-cgi"
+
+
+def test_dns_zone_lookup(client: ISPConfigClient) -> None:
+    zone_id = client.dns.zone_get_id("mcbindustrial.com.")
+    assert zone_id > 0, "zone_get_id returned 0 — is the zone present?"
+
+
+def test_mail_users_under_mcbindustrial(client: ISPConfigClient) -> None:
+    # mail_user_get accepts a filter-dict and returns a list.
+    users = client.mail.user_get({"email": "%@mcbindustrial.com"})
+    assert isinstance(users, list)
+    # Don't assert count — just shape. Zero mailboxes is a valid state.
+    for u in users:
+        assert "email" in u