fix: make paragraph refactor service use configured AI provider

The paragraph-refactor service was using OLLAMA_BASE_URL directly from
environment variables instead of using the configured AI provider from
the database. This caused "OLLAMA error" even when OpenAI was configured
in the admin interface.

Changes:
- paragraph-refactor.service.ts: Now uses getSystemConfig() and
  getTagsProvider() from factory instead of direct Ollama calls
- factory.ts: Added proper error messages when API keys are missing
- .env.docker.example: Updated with new provider configuration
  variables (AI_PROVIDER_TAGS, AI_PROVIDER_EMBEDDING)

This fixes the issue where AI reformulation features (Clarify, Shorten,
Improve Style) would fail with OLLAMA errors even when OpenAI was
properly configured in the admin settings.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

keep-notes/prisma/client-generated/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "prisma-client-62aaff0ff1302a5b1470021854f34bb9a9c1219fe39a7ee39aa626bd83e22eae",
+  "name": "prisma-client-46efe72656f1c393bbd99fdd6d2d34037b30f693f014757faf08aec1d9319858",
   "main": "index.js",
   "types": "index.d.ts",
   "browser": "index-browser.js",