feat: driver rename, driver icons, web image + driver search

Driver rename and icons: `Driver.display_name` plus a `DriverIcon` table, both
global/shared like the `Driver` row they hang off, so a rename or an icon is
what every Owner sees. The rename/icon dialog keeps its forms as siblings
(nested forms are invalid HTML) and the icon routes return an `hx-swap-oob`
thumbnail refresh rather than re-rendering the table, which would tear the open
`<dialog>` out of the DOM.

Web image picker: `GET /web/images` renders a pickable grid for a printer or a
driver icon, with the search term prefilled from the entity name and editable.
Picking one downloads it server-side and normalizes it.

Driver download search: `GET /web/drivers` searches for a vendor-wide driver
(the term is rewritten into the vendor's real product name for 15 brands) or for
the exact model as typed. Links only — nothing is downloaded, and the fragment
says the results are unvetted.

Icon uploads no longer reject off-size or non-PNG files: `normalize_icon()`
letterboxes any decodable raster into a 256x256 PNG. An already-exact 256x256
PNG is returned byte-identical, because icon storage is content-addressed and
re-encoding would move the file on every save.

`fetch_image()` makes the request from the server, so `assert_fetchable()`
refuses any URL resolving to a private, loopback, or link-local address, and
re-runs on every redirect. ImpTune sits on the same LAN as the printers it
configures; an unguarded fetcher would be a port scanner for anyone who can
reach the UI.

DuckDuckGo is scraped, not called through an API — no key needed, but fragile,
so both search functions swallow parse failures and return [] instead of 500ing
a page. `WEB_SEARCH=false` disables every outbound request and hides the
controls, for air-gapped installs.

Also: one shared `Jinja2Templates` in `templating.py` instead of five per-router
instances, so a template global is declared once; `_add_missing_columns()` in
`database.py` adds new nullable columns to a pre-existing table, which
`create_tables(safe=True)` skips; `db_env` in test_db.py now closes its
connection on teardown, or the next test's ORM writes land in the previous
test's DB file.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

imptune/api/printers.py

@@ -1,22 +1,16 @@
 """Printer CRUD API — POST /printers, DELETE /printers/{id}, PATCH /printers/{id}."""
 from __future__ import annotations
 
-from pathlib import Path
-
 from fastapi import APIRouter, Form, Request
 from fastapi.responses import HTMLResponse, RedirectResponse, Response
-from fastapi.templating import Jinja2Templates
 from peewee import JOIN
 
-from imptune.api.pages import group_printers_by_client
+from imptune.api.pages import build_driver_data, group_printers_by_client
 from imptune.db.models import Client, Driver, Printer
+from imptune.templating import templates
 
 router = APIRouter(prefix="/printers")
 
-templates = Jinja2Templates(
-    directory=str(Path(__file__).parent.parent / "templates")
-)
-
 _VALID_DUPLEX = {"OneSided", "LongEdge", "ShortEdge"}
 _VALID_PAPER = {"A4", "Letter", "Legal"}
 
@@ -84,8 +78,6 @@ def _resolve_driver(raw: str) -> tuple[int | None, HTMLResponse | None]:
 
 def _render_printer_list(request: Request) -> HTMLResponse:
     """Query printers with LEFT JOIN on client and render grouped partial."""
-    import json
-
     owner = request.state.owner
     query = (
         Printer.select(Printer, Client)
@@ -96,11 +88,8 @@ def _render_printer_list(request: Request) -> HTMLResponse:
     grouped = group_printers_by_client(query)
 
     clients = list(Client.select().where(Client.owner == owner).order_by(Client.name))
-    all_drivers = list(Driver.select().order_by(Driver.uploaded_at.desc()))
-    driver_data = [
-        {"driver": d, "names": json.loads(d.driver_desc) if d.driver_desc else []}
-        for d in all_drivers
-    ]
+    all_drivers = Driver.select().order_by(Driver.uploaded_at.desc())
+    driver_data = build_driver_data(all_drivers)
 
     return templates.TemplateResponse(
         request=request,