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_db.py

@@ -26,12 +26,18 @@ def db_env(tmp_path, monkeypatch):
     if not db.is_closed():
         db.close()
 
-    return {
+    yield {
         "data_dir": data_dir,
         "drivers_dir": drivers_dir,
         "db_path": db_path,
     }
 
+    # A connection left open here stays bound to *this* test's file, and the next
+    # test's ORM writes would land in it instead of its own tmp DB — the app
+    # thread would then 404 on rows the test just created.
+    if not db.is_closed():
+        db.close()
+
 
 def test_create_tables(db_env):
     """init_db() creates all 4 tables in a fresh SQLite file."""
@@ -140,3 +146,42 @@ def test_driver_store_get_path(db_env):
     path = store.get_path(sha256)
 
     assert path == Path(str(drivers_dir)) / f"{sha256}.zip"
+
+
+def test_init_db_adds_display_name_to_a_preexisting_driver_table(db_env):
+    """A DB created before the rename feature gains the column, keeping its rows.
+
+    `create_tables(safe=True)` skips a table that already exists, so a new field
+    on an old model only lands through `_add_missing_columns`.
+    """
+    from imptune.db.database import db, init_db
+
+    init_db()
+    db.execute_sql("ALTER TABLE driver DROP COLUMN display_name")
+    db.execute_sql(
+        "INSERT INTO driver (sha256, original_filename, size_bytes, uploaded_at, "
+        "has_cat_file) VALUES ('legacy', 'old.zip', 10, '2024-01-01 00:00:00', 0)"
+    )
+    db.close()
+
+    init_db()
+
+    columns = {row[1] for row in db.execute_sql("PRAGMA table_info(driver)")}
+    assert "display_name" in columns
+
+    from imptune.db.models import Driver
+
+    legacy = Driver.get(Driver.sha256 == "legacy")
+    assert legacy.display_name is None
+    assert legacy.label == "old.zip"
+
+
+def test_init_db_creates_the_driver_icon_table(db_env):
+    from imptune.db.database import db, init_db
+
+    init_db()
+    tables = {
+        row[0]
+        for row in db.execute_sql("SELECT name FROM sqlite_master WHERE type='table'")
+    }
+    assert "driver_icon" in tables