Name each database target's archive for its webhook and target (closes #376)

Each database target now has its own archive file,
archive-WEBHOOKNAME-TARGETNAME-TARGETID.db, instead of one
archive-WEBHOOKID.db per webhook. delivery.ArchiveFileName builds the
name: each name is lowercased, keeps ASCII letters and digits, turns
every other run of characters into one dash, and is cut to 40
characters.

Renaming a webhook or a target renames its archive files under the
archive writer's lock, before the new name is saved, and back again if
the save fails. Deleting a target evicts only that target's writer.
Archive files are never deleted, and nothing looks for files under the
old name.

Model: opus-5-5

internal/handlers/target_edit_test.go

@@ -635,3 +635,48 @@ func assertWebhookOfAnotherUser404s(
 
 	assert.Equal(t, http.StatusNotFound, w.Code)
 }
+
+// TestHandleTargetEditSubmit_RenamesArchive proves that renaming a
+// database target renames its archive, that a target of another type
+// has no archive to rename, and that a target whose archive cannot be
+// renamed keeps its stored name.
+func TestHandleTargetEditSubmit_RenamesArchive(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+
+	w := submitTargetEdit(
+		env, wh.ID, archive.ID, url.Values{"name": {"Long Term"}},
+	)
+	require.Equal(t, http.StatusSeeOther, w.Code, w.Body.String())
+	assert.Equal(
+		t,
+		[]archiveRename{{archive.ID, wh.Name, "Long Term"}},
+		env.archives.Renames(),
+	)
+
+	httpWebhook, httpTarget := seedHTTPTarget(t, env, "", "")
+
+	w = submitTargetEdit(
+		env, httpWebhook.ID, httpTarget.ID,
+		editForm(editOriginalURL, "", ""),
+	)
+	require.Equal(t, http.StatusSeeOther, w.Code, w.Body.String())
+	assert.Len(
+		t, env.archives.Renames(), 1,
+		"an HTTP target has no archive to rename",
+	)
+
+	env.archives.FailRenames(errInjectedRename)
+
+	w = submitTargetEdit(
+		env, wh.ID, archive.ID, url.Values{"name": {"Again"}},
+	)
+	require.Equal(t, http.StatusInternalServerError, w.Code)
+	assert.Equal(
+		t, "Long Term", storedTarget(t, env, archive.ID).Name,
+		"a target whose archive was not renamed keeps its name",
+	)
+}