fix: bundle chromadb and fix fetch invocation in Electron

- Bundle chromadb into main.js via esbuild instead of externalizing it.
  Obsidian's renderer cannot resolve bare require('chromadb') against a
  plugin-local node_modules. By bundling, the client library is inlined and
  works out of the box with just manifest.json + main.js.

- Remove eager cache initialization from OllamaClient constructor to avoid
  unhandled promise rejections when chromadb/ChromaDB is unavailable.

- Fix 'Failed to execute fetch on Window: Illegal invocation' by wrapping
  the default fetch fallback in an arrow function:
    this.fetchFn = fetchFn ?? ((url, init) => fetch(url, init));
  This preserves the window binding when fetch is called later.

- Update install.sh and README to remove the obsolete node_modules/chromadb
  copy step.

- Update ollama-client-cache tests to reflect that cache initialization is
  no longer eager.

package.json

@@ -5,7 +5,7 @@
   "main": "dist/main.js",
   "scripts": {
     "test": "jest",
-    "build": "tsc --noEmit && node -e \"require('esbuild').build({entryPoints:['src/main.ts'],bundle:true,platform:'node',target:'es2020',outfile:'main.js',external:['obsidian','chromadb'],format:'cjs'})\"",
+    "build": "tsc --noEmit && node -e \"require('esbuild').build({entryPoints:['src/main.ts'],bundle:true,platform:'node',target:'es2020',outfile:'main.js',external:['obsidian','cohere-ai','ollama','openai','@google/generative-ai','voyageai'],format:'cjs'})\"",
     "watch": "tsc --watch",
     "lint": "eslint src --ext .ts",
     "format": "prettier --write ."