feat: add PATCH /tags/{id}/rules/{then_id} to activate/deactivate rules

- openapi.yaml: new PATCH endpoint with is_active body, returns TagRule
- backend/service: SetRuleActive calls repo.SetActive then returns updated rule
- backend/handler: PatchRule validates body and delegates to service
- backend/router: register PATCH /:tag_id/rules/:then_tag_id
- frontend: TagRuleEditor uses PATCH instead of delete+recreate
- mock: handle PATCH /tags/{id}/rules/{then_id}

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/tag/TagRuleEditor.svelte

@@ -62,13 +62,9 @@
 		busy = true;
 		error = '';
 		const thenTagId = rule.then_tag_id!;
-		const newActive = !rule.is_active;
 		try {
-			await api.delete(`/tags/${tagId}/rules/${thenTagId}`);
-			const updated = await api.post<TagRule>(`/tags/${tagId}/rules`, {
-				then_tag_id: thenTagId,
-				is_active: newActive,
-				apply_to_existing: false,
+			const updated = await api.patch<TagRule>(`/tags/${tagId}/rules/${thenTagId}`, {
+				is_active: !rule.is_active,
 			});
 			onRulesChange(rules.map((r) => r.then_tag_id === thenTagId ? updated : r));
 		} catch (e) {

frontend/vite-mock-plugin.ts

@@ -402,6 +402,19 @@ export function mockApiPlugin(): Plugin {
 					return json(res, 201, { tag_id: tid, then_tag_id: thenId, then_tag_name: t?.name ?? null, is_active: isActive });
 				}
 
+				// PATCH /tags/{id}/rules/{then_id}  — activate / deactivate
+				const tagRulesPatchMatch = path.match(/^\/tags\/([^/]+)\/rules\/([^/]+)$/);
+				if (method === 'PATCH' && tagRulesPatchMatch) {
+					const [, tid, thenId] = tagRulesPatchMatch;
+					const body = (await readBody(req)) as Record<string, unknown>;
+					const isActive = body.is_active as boolean;
+					const ruleMap = tagRules.get(tid);
+					if (!ruleMap?.has(thenId)) return json(res, 404, { code: 'not_found', message: 'Rule not found' });
+					ruleMap.set(thenId, isActive);
+					const t = MOCK_TAGS.find((x) => x.id === thenId);
+					return json(res, 200, { tag_id: tid, then_tag_id: thenId, then_tag_name: t?.name ?? null, is_active: isActive });
+				}
+
 				// DELETE /tags/{id}/rules/{then_id}
 				const tagRulesDelMatch = path.match(/^\/tags\/([^/]+)\/rules\/([^/]+)$/);
 				if (method === 'DELETE' && tagRulesDelMatch) {