fix(web): convert visibility enum values to string names in filter expressions

Problem:
The Explore page filter was sending visibility filter as:
  visibility in ["3", "2"]
when it should send:
  visibility in ["PUBLIC", "PROTECTED"]

The backend CEL filter parser expects string enum names, not numeric values.
This caused the Explore page to return no memos even when public memos existed.

Solution:
- Added getVisibilityName() helper to convert Visibility enum values to string names
- Updated useMemoFilters to use getVisibilityName() when building visibility filter
- Follows same pattern as existing getInstanceSettingKeyName() and getUserSettingKeyName()
- Added validation to warn on invalid enum values

Files changed:
- web/src/store/common.ts: Add getVisibilityName() helper with validation
- web/src/hooks/useMemoFilters.ts: Use getVisibilityName() in visibility filter

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web/src/hooks/useMemoFilters.ts

 import { useMemo } from "react";
 import { instanceStore, userStore } from "@/store";
-import { extractUserIdFromName } from "@/store/common";
+import { extractUserIdFromName, getVisibilityName } from "@/store/common";
 import memoFilterStore from "@/store/memoFilter";
 import { InstanceSetting_Key } from "@/types/proto/api/v1/instance_service_pb";
 import { Visibility } from "@/types/proto/api/v1/memo_service_pb";
@@ -81,7 +81,8 @@ export const useMemoFilters = (options: UseMemoFiltersOptions = {}): string | un
     if (visibilities && visibilities.length > 0) {
       // Build visibility filter based on allowed visibility levels
       // Format: visibility in ["PUBLIC", "PROTECTED"]
-      const visibilityValues = visibilities.map((v) => `"${v}"`).join(", ");
+      // Convert enum values to string names (e.g., 3 -> "PUBLIC", 2 -> "PROTECTED")
+      const visibilityValues = visibilities.map((v) => `"${getVisibilityName(v)}"`).join(", ");
       conditions.push(`visibility in [${visibilityValues}]`);
     }
 

web/src/store/common.ts

 import { InstanceSetting_Key } from "@/types/proto/api/v1/instance_service_pb";
+import { Visibility } from "@/types/proto/api/v1/memo_service_pb";
 import { UserSetting_Key } from "@/types/proto/api/v1/user_service_pb";
 
 export const instanceSettingNamePrefix = "instance/settings/";
@@ -40,3 +41,17 @@ export const getUserSettingKeyName = (key: UserSetting_Key): string => {
 export const buildUserSettingName = (username: string, key: UserSetting_Key): string => {
   return `${username}/settings/${getUserSettingKeyName(key)}`;
 };
+
+// Helper function to convert Visibility enum value to string name
+// Used when building filter expressions that require string enum names instead of numeric values
+// Example: visibility in ["PUBLIC", "PROTECTED"] instead of visibility in ["3", "2"]
+export const getVisibilityName = (visibility: Visibility): string => {
+  // TypeScript enum reverse mapping: converts numeric value to string name
+  // e.g., Visibility.PUBLIC (3) -> "PUBLIC"
+  const name = Visibility[visibility];
+  if (!name) {
+    console.warn(`Invalid visibility value: ${visibility}, defaulting to PUBLIC`);
+    return "PUBLIC";
+  }
+  return name;
+};