feat(03-01): implement printer and client CRUD with HTMX/Alpine.js UI

- imptune/api/printers.py: POST /printers (all form fields, checkbox->bool,
  FK resolution), DELETE /printers/{id}, grouped list renderer with LEFT JOIN
- imptune/api/clients.py: POST /clients with duplicate-name handling
- imptune/api/pages.py: GET /printers and GET /clients page routes
- imptune/main.py: register printers + clients routers; close db on shutdown
- imptune/db/database.py: close existing connection before re-init (test isolation)
- templates: printers.html, clients.html, printer_form.html (Alpine.js port
  auto-derivation), printer_list.html (grouped by client), client_list.html
- tests/conftest.py: close test-thread db connection in fixture teardown
- tests/test_printer_crud.py: updated to use list(select().where()) for DB
  queries (avoids Peewee thread-local cursor caching across test boundaries)

Auto-fix [Rule 1 - Bug]: DB test isolation — Peewee thread-local connections
persisted across tests causing stale DB reads; fixed via conftest teardown and
lifespan db.close() on shutdown.

imptune/api/pages.py

@@ -1,9 +1,11 @@
 import json
+from collections import defaultdict
+from pathlib import Path
 
 from fastapi import APIRouter, Request
 from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
-from pathlib import Path
+from peewee import JOIN
 
 router = APIRouter()
 
@@ -36,3 +38,48 @@ def drivers_page(request: Request):
         name="drivers.html",
         context={"driver_data": driver_data},
     )
+
+
+@router.get("/printers", response_class=HTMLResponse)
+def printers_page(request: Request):
+    from imptune.db.models import Client, Driver, Printer
+
+    query = (
+        Printer.select(Printer, Client)
+        .join(Client, JOIN.LEFT_OUTER)
+        .order_by(Client.name, Printer.name)
+    )
+    grouped: dict[str, list] = defaultdict(list)
+    for p in query:
+        client_name = p.client.name if p.client_id else "Unassigned"
+        grouped[client_name].append(p)
+
+    clients = list(Client.select().order_by(Client.name))
+
+    all_drivers = list(Driver.select().order_by(Driver.uploaded_at.desc()))
+    driver_data = []
+    for d in all_drivers:
+        names = json.loads(d.driver_desc) if d.driver_desc else []
+        driver_data.append({"driver": d, "names": names})
+
+    return templates.TemplateResponse(
+        request=request,
+        name="printers.html",
+        context={
+            "grouped": grouped,
+            "clients": clients,
+            "driver_data": driver_data,
+        },
+    )
+
+
+@router.get("/clients", response_class=HTMLResponse)
+def clients_page(request: Request):
+    from imptune.db.models import Client
+
+    clients = list(Client.select().order_by(Client.name))
+    return templates.TemplateResponse(
+        request=request,
+        name="clients.html",
+        context={"clients": clients},
+    )