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.

tests/conftest.py

@@ -24,4 +24,12 @@ def tmp_data_dir(tmp_path, monkeypatch):
     cfg.DATA_DIR = str(data_dir)
     cfg.DB_PATH = str(data_dir / "imptune.db")
     cfg.DRIVERS_DIR = str(data_dir / "drivers")
-    return data_dir
+
+    yield data_dir
+
+    # Close the test-thread's DB connection so the next test gets a fresh one
+    # pointing to its own tmp DB (Peewee connections are thread-local).
+    from imptune.db.database import db
+
+    if not db.is_closed():
+        db.close()

tests/test_printer_crud.py

@@ -47,8 +47,9 @@ def test_create_printer_duplex(client: TestClient) -> None:
     )
     assert resp.status_code == 200
 
-    printer = Printer.get(Printer.name == "Duplex Printer")
-    assert printer.duplex_mode == "LongEdge"
+    printers = list(Printer.select().where(Printer.name == "Duplex Printer"))
+    assert len(printers) == 1
+    assert printers[0].duplex_mode == "LongEdge"
 
 
 def test_create_printer_color_mode(client: TestClient) -> None:
@@ -66,8 +67,9 @@ def test_create_printer_color_mode(client: TestClient) -> None:
     )
     assert resp.status_code == 200
 
-    printer = Printer.get(Printer.name == "Mono Printer")
-    assert printer.color_mode is False
+    printers = list(Printer.select().where(Printer.name == "Mono Printer"))
+    assert len(printers) == 1
+    assert printers[0].color_mode is False
 
 
 def test_create_printer_paper_size(client: TestClient) -> None:
@@ -85,8 +87,9 @@ def test_create_printer_paper_size(client: TestClient) -> None:
     )
     assert resp.status_code == 200
 
-    printer = Printer.get(Printer.name == "Letter Printer")
-    assert printer.paper_size == "Letter"
+    printers = list(Printer.select().where(Printer.name == "Letter Printer"))
+    assert len(printers) == 1
+    assert printers[0].paper_size == "Letter"
 
 
 def test_create_printer_collate(client: TestClient) -> None:
@@ -104,8 +107,9 @@ def test_create_printer_collate(client: TestClient) -> None:
     )
     assert resp.status_code == 200
 
-    printer = Printer.get(Printer.name == "No Collate Printer")
-    assert printer.collate is False
+    printers = list(Printer.select().where(Printer.name == "No Collate Printer"))
+    assert len(printers) == 1
+    assert printers[0].collate is False
 
 
 def test_create_client(client: TestClient) -> None:
@@ -126,7 +130,9 @@ def test_printer_grouped_by_client(client: TestClient) -> None:
     resp = client.post("/clients", data={"name": "Contoso"})
     assert resp.status_code == 200
 
-    contoso = Client.get(Client.name == "Contoso")
+    contoso_list = list(Client.select().where(Client.name == "Contoso"))
+    assert len(contoso_list) == 1
+    contoso = contoso_list[0]
 
     # Create printer assigned to that client
     resp = client.post(
@@ -191,8 +197,9 @@ def test_delete_printer(client: TestClient) -> None:
     assert resp.status_code == 200
 
     # Find its ID
-    printer = Printer.get(Printer.name == "To Delete")
-    printer_id = printer.id
+    printers = list(Printer.select().where(Printer.name == "To Delete"))
+    assert len(printers) == 1
+    printer_id = printers[0].id
 
     # Delete it
     resp = client.delete(f"/printers/{printer_id}")