Feat: Prepare frontend future model

Frontend/src/styles/user-overrides.scss

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+/* Path: Frontend/src/styles/user-overrides.scss */
+
+/*
+	Optional global frontend override seam.
+
+	This file is imported after the core app styles so user or deployment-specific
+	overrides can layer on top without reshaping component code first.
+
+	Examples for later:
+	- import a tenant branding bundle
+	- apply a self-hosted custom theme
+	- override shared shell spacing or color tokens
+	- target stable `data-ui`, `data-slot`, or state attributes added in the app shell
+
+	You can either place raw overrides here directly or layer another stylesheet:
+
+	@use "./my-brand" as *;
+*/
+
+/*
+	Stable override hooks are intentionally exposed with global data attributes so
+	manual overrides do not depend on CSS module hash names.
+
+	Examples:
+
+	[data-ui="top-bar"] {
+		backdrop-filter: blur(24px);
+	}
+
+	[data-ui="workspace-sidebar"] [data-slot="workspace-tree-item"][data-kind="item"] {
+		border-radius: 12px;
+	}
+
+	[data-ui="workspace-context-menu"] [data-action-id="delete"] {
+		letter-spacing: 0.01em;
+	}
+
+	[data-ui="notifications-menu"][data-variant="workspace"] {
+		max-width: none;
+	}
+*/