Modernize web client: dark phase-driven theme, sidebar shell, global agent panel

Replaces the warm-paper/serif look with a dark palette where the novel's
lifecycle phase drives the accent color app-wide. Sidebar nav replaces the
old header/tab-bar. Dashboard leads with quick actions (new chapter, new
character, continue writing) instead of just showing history. Agent chat
is now a context-aware slide-out panel reachable from any page in a novel,
replacing the buried /agent tab.

src/Novelly.Web/package-lock.json

@@ -8,6 +8,10 @@
       "name": "novelly-web",
       "version": "0.0.0",
       "dependencies": {
+        "@fontsource-variable/fraunces": "^5.3.0",
+        "@fontsource-variable/inter": "^5.3.0",
+        "@fontsource-variable/source-serif-4": "^5.3.0",
+        "@fontsource/jetbrains-mono": "^5.3.0",
         "@tanstack/react-query": "^5.101.4",
         "react": "^19.2.8",
         "react-dom": "^19.2.8",
@@ -27,6 +31,38 @@
         "vite": "^8.2.0"
       }
     },
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+      "version": "5.3.0",
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+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
+    },
+    "node_modules/@fontsource-variable/inter": {
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/@fontsource-variable/inter/-/inter-5.3.0.tgz",
+      "integrity": "sha512-OupL48va4JNofb97w6NYeF9S7W/kHNKM0Er8Dem5nqi4jeOLrVJDoE8tZEpnMJmtkvNbB1EIPPwHcdkF6b1oUA==",
+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
+    },
+    "node_modules/@fontsource-variable/source-serif-4": {
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/@fontsource-variable/source-serif-4/-/source-serif-4-5.3.0.tgz",
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+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
+    },
+    "node_modules/@fontsource/jetbrains-mono": {
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/@fontsource/jetbrains-mono/-/jetbrains-mono-5.3.0.tgz",
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+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
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     "node_modules/@jridgewell/gen-mapping": {
       "version": "0.3.13",
       "resolved": "https://registry.npmjs.org/@jridgewell/gen-mapping/-/gen-mapping-0.3.13.tgz",