feat(hermes): replace Prompts entry with Memory panel

Hermes has no slash-prompt concept (templates live as Skills), so the
Prompts tab for the Hermes app was always empty. Swap the toolbar Book
button for a Brain button that opens a new Memory panel editing
~/.hermes/memories/{MEMORY,USER}.md — Hermes' first-class memory store
which its Web UI exposes only as on/off toggles, never as an editor.

The panel shows each file in its own tab with a character-budget bar
read from config.yaml's nested memory.* section (memory_char_limit /
user_char_limit, default 2200 / 1375). Edits are written atomically;
Hermes picks them up on the next session start per MemoryStore.

Also extract useDarkMode to src/hooks/useDarkMode.ts — the codebase
already repeats the same MutationObserver pattern in 12+ places; this
PR introduces the shared hook and uses it once, leaving the migration
of the other copies to a follow-up.

src/i18n/locales/en.json

@@ -1675,6 +1675,19 @@
       "parseFailed": "config.yaml could not be parsed as valid YAML. Fix the file before editing it here.",
       "configNotFound": "Hermes config.yaml not found. Create it at ~/.hermes/config.yaml or configure the path in settings.",
       "envParseFailed": "The .env file could not be parsed."
+    },
+    "memory": {
+      "title": "Memory",
+      "agentTab": "Agent Memory (MEMORY.md)",
+      "userTab": "User Profile (USER.md)",
+      "usage": "{{current}} / {{limit}} characters",
+      "overLimit": "Over budget — Hermes will truncate on next load",
+      "disabled": "Memory is disabled in config.yaml. Enable it in Hermes config for edits to take effect.",
+      "saveSuccess": "Memory saved",
+      "saveFailed": "Failed to save memory",
+      "loadFailed": "Failed to read memory file",
+      "openConfig": "Adjust limits in Hermes Web UI",
+      "runtimeNote": "Changes apply on Hermes restart or new session."
     }
   },
   "env": {

src/i18n/locales/ja.json

@@ -1675,6 +1675,19 @@
       "parseFailed": "config.yaml を有効な YAML として解析できません。ここで編集する前にファイルを修正してください。",
       "configNotFound": "Hermes config.yaml が見つかりません。~/.hermes/config.yaml に作成するか、設定でパスを構成してください。",
       "envParseFailed": ".env ファイルを解析できません。"
+    },
+    "memory": {
+      "title": "メモリ",
+      "agentTab": "エージェント記憶 (MEMORY.md)",
+      "userTab": "ユーザープロファイル (USER.md)",
+      "usage": "{{current}} / {{limit}} 文字",
+      "overLimit": "上限を超えました。Hermes は次回読み込み時に切り詰めます",
+      "disabled": "Memory が config.yaml で無効化されています。Hermes 設定で有効化すると編集内容が反映されます。",
+      "saveSuccess": "記憶を保存しました",
+      "saveFailed": "記憶の保存に失敗しました",
+      "loadFailed": "記憶ファイルの読み込みに失敗しました",
+      "openConfig": "Hermes Web UI で上限を調整",
+      "runtimeNote": "変更は Hermes の再起動または新規セッション時に反映されます。"
     }
   },
   "env": {

src/i18n/locales/zh.json

@@ -1675,6 +1675,19 @@
       "parseFailed": "config.yaml 无法解析为有效 YAML。请先修复文件再在此编辑。",
       "configNotFound": "未找到 Hermes config.yaml。请在 ~/.hermes/config.yaml 创建或在设置中配置路径。",
       "envParseFailed": ".env 文件无法解析。"
+    },
+    "memory": {
+      "title": "记忆管理",
+      "agentTab": "Agent 记忆 (MEMORY.md)",
+      "userTab": "用户画像 (USER.md)",
+      "usage": "已用 {{current}} / {{limit}} 字符",
+      "overLimit": "已超过上限，Hermes 下次加载时会截断",
+      "disabled": "Memory 在 config.yaml 中已禁用，编辑后需在 Hermes 配置启用才会生效。",
+      "saveSuccess": "记忆已保存",
+      "saveFailed": "保存记忆失败",
+      "loadFailed": "读取记忆文件失败",
+      "openConfig": "在 Hermes Web UI 调整上限",
+      "runtimeNote": "更改将在 Hermes 下次启动或新建会话时生效。"
     }
   },
   "env": {