Disable svelte/prefer-svelte-reactivity (SvelteDate purge rationale)

The rule pushes SvelteDate (svelte/reactivity), which this codebase
deliberately removed in 55b2c8c because it caused real bugs. All Date usage is
local wall-clock computation via parseWallClockDate helpers, not reactive
$state Date mutations, and the rule has no options to allowlist Date — so
disable it outright in the svelte block with a rationale comment. Restores a
clean eslint gate for the pre-commit hook and CI.

frontend/eslint.config.js

@@ -52,6 +52,13 @@ export default defineConfig(
 				svelteConfig
 			}
 		},
-		rules: {}
+		rules: {
+			// The prefer-svelte-reactivity rule pushes SvelteDate (svelte/reactivity), which this
+			// codebase deliberately removed (commit 55b2c8c, "SvelteDate→Date purge") because it
+			// caused real bugs. All Date usage here is local wall-clock computation (the
+			// parseWallClockDate helpers in src/lib/utils/timeSlots.ts), not reactive $state Date
+			// mutations, and the rule has no options to allowlist Date — so disable it outright.
+			'svelte/prefer-svelte-reactivity': 'off'
+		}
 	}
 );