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>

tests/test_icon_upload.py

@@ -66,16 +66,35 @@ class TestIconUpload:
         icon_file = Path(tmp_data_dir) / "icons" / sha256
         assert icon_file.exists()
 
-    def test_reject_non_png(self, client, owner, tmp_data_dir):
-        """POST with a JPEG file returns 422 with PNG format error."""
+    def test_jpeg_is_converted(self, client, owner, tmp_data_dir):
+        """A JPEG is accepted and re-encoded as a 256x256 PNG, not rejected."""
+        from pathlib import Path
+
+        from imptune.db.models import Icon
+
         printer = _create_printer(owner)
         jpeg_data = _make_jpeg(256, 256)
         response = client.post(
             f"/printers/{printer.id}/icon",
             files={"file": ("icon.jpg", io.BytesIO(jpeg_data), "image/jpeg")},
         )
+        assert response.status_code == 200
+
+        icon = Icon.get(Icon.printer == printer.id)
+        stored = Path(tmp_data_dir) / "icons" / icon.sha256
+        with Image.open(stored) as img:
+            assert img.format == "PNG"
+            assert img.size == (256, 256)
+
+    def test_reject_undecodable_file(self, client, owner, tmp_data_dir):
+        """A file Pillow cannot open is still refused."""
+        printer = _create_printer(owner)
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("icon.png", io.BytesIO(b"not an image at all"), "image/png")},
+        )
         assert response.status_code == 422
-        assert "PNG" in response.text
+        assert "readable image" in response.text
 
     def test_reject_oversized(self, client, owner, tmp_data_dir):
         """POST with PNG > 750KB returns 422 with 750 KB error."""
@@ -90,16 +109,24 @@ class TestIconUpload:
         assert response.status_code == 422
         assert "750" in response.text
 
-    def test_reject_wrong_dimensions(self, client, owner, tmp_data_dir):
-        """POST with 128x128 PNG returns 422 with 256x256 error."""
+    def test_wrong_dimensions_are_resized(self, client, owner, tmp_data_dir):
+        """An off-size PNG is letterboxed into 256x256 instead of rejected."""
+        from pathlib import Path
+
+        from imptune.db.models import Icon
+
         printer = _create_printer(owner)
-        png_data = _make_png(128, 128)
+        png_data = _make_png(128, 400)
         response = client.post(
             f"/printers/{printer.id}/icon",
-            files={"file": ("small.png", io.BytesIO(png_data), "image/png")},
+            files={"file": ("tall.png", io.BytesIO(png_data), "image/png")},
         )
-        assert response.status_code == 422
-        assert "256x256" in response.text
+        assert response.status_code == 200
+
+        icon = Icon.get(Icon.printer == printer.id)
+        stored = Path(tmp_data_dir) / "icons" / icon.sha256
+        with Image.open(stored) as img:
+            assert img.size == (256, 256)
 
     def test_replace_existing_icon(self, client, owner, tmp_data_dir):
         """Second upload for same printer replaces the Icon record."""