chore: move sqlite-vec to optionalDependencies, fix js-tiktoken static import

Both changes ensure native binary dependencies are properly categorized as optional:

- sqlite-vec: moved from dependencies to optionalDependencies. Only used via
  lazy _require("sqlite-vec") in vectorStore.ts — zero static imports.
- js-tiktoken: already in optionalDependencies, import changed to createRequire
  pattern to avoid crash when package is not installed (same pattern as sqlite-vec
  in vectorStore.ts).

Resolves ScoutDeps findings from browser-pool pluginization audit.

package.json

@@ -304,7 +304,6 @@
     "smol-toml": "1.7.1",
     "socks": "^2.8.7",
     "sql.js": "^1.14.1",
-    "sqlite-vec": "^0.1.9",
     "tailwind-merge": "^3.6.0",
     "tsx": "^4.23.0",
     "undici": "^8.3.0",
@@ -324,7 +323,8 @@
     "js-tiktoken": "^1.0.20",
     "keytar": "^7.9.0",
     "tls-client-node": "^0.2.0",
-    "wreq-js": "^2.3.1"
+    "wreq-js": "^2.3.1",
+    "sqlite-vec": "^0.1.9"
   },
   "devDependencies": {
     "@axe-core/playwright": "^4.11.3",

src/shared/utils/tiktokenCounter.ts

@@ -1,4 +1,7 @@
-import { getEncoding, type Tiktoken } from "js-tiktoken";
+import type { Tiktoken } from "js-tiktoken";
+import { createRequire } from "module";
+
+const _require = createRequire(import.meta.url);
 
 export type TokenizerEncoding = "cl100k_base" | "o200k_base";
 
@@ -41,9 +44,15 @@ export function resolveTokenizerEncoding(context?: TokenizerContext): TokenizerE
 function getEncoder(encoding: TokenizerEncoding): Tiktoken {
   const cached = encoders.get(encoding);
   if (cached) return cached;
-  const created = getEncoding(encoding);
-  encoders.set(encoding, created);
-  return created;
+  let tiktoken: { getEncoding: (name: string) => Tiktoken } | null = null;
+  try {
+    tiktoken ??= _require("js-tiktoken") as { getEncoding: (name: string) => Tiktoken };
+    const created = tiktoken.getEncoding(encoding);
+    encoders.set(encoding, created);
+    return created;
+  } catch {
+    throw new Error(`js-tiktoken not available: cannot create encoder for ${encoding}`);
+  }
 }
 
 /**