polish: replace sidebar Unicode glyphs with Lucide icons

The Unicode/symbol icons (◈ ☰ ▶ ⌕ ⟐ ✦ …) rendered inconsistently across
platforms and sizes. Lucide is crisp and pixel-perfect at any zoom.

- Add lucide-react (pinned exact); tree-shakes to the 15 icons used.
- NAV_ITEMS is now NavItem[] with ReactNode icons (the as-const array
  couldn't carry JSX). View type exported from the ui store for it.
- Icon spans switched from text-centred glyphs to flex-centred SVGs.
- Write-article ✦ -> PenLine.

package-lock.json

@@ -23,6 +23,7 @@
         "@types/dompurify": "^3.0.5",
         "dompurify": "^3.4.0",
         "highlight.js": "^11.11.1",
+        "lucide-react": "1.16.0",
         "marked": "^17.0.4",
         "marked-highlight": "^2.2.3",
         "react": "^19.1.0",
@@ -3585,6 +3586,15 @@
         "yallist": "^3.0.2"
       }
     },
+    "node_modules/lucide-react": {
+      "version": "1.16.0",
+      "resolved": "https://registry.npmjs.org/lucide-react/-/lucide-react-1.16.0.tgz",
+      "integrity": "sha512-dYwyPzb4MEKpGUmNYk3WKWPnMrHs3FKM+q94kAnJrcDIqqn1hq2xY8scaS2ovsOCM5D51ey2gaRG3PBb1vgoYQ==",
+      "license": "ISC",
+      "peerDependencies": {
+        "react": "^16.5.1 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/lz-string": {
       "version": "1.5.0",
       "resolved": "https://registry.npmjs.org/lz-string/-/lz-string-1.5.0.tgz",