Bugfixes/nextclou ai

[pledou]

This pull request updates the Nextcloud integration to improve how embedding models are managed and used for context chat features. The main focus is on ensuring the correct embedding model (nomic-embed-text) is consistently configured, reliably pulled into the Ollama Embeddings instance, and properly referenced by the context chat backend. Additionally, a networking fix is applied to ensure ExApps are accessible over both IPv4 and IPv6.

Embedding model improvements:

• Set the default embedding model for context chat to nomic-embed-text in main.yml, with comments explaining the rationale and issues with alternative models.
• Updated ExApp backend configuration to use the embedding model variable and adjusted the embedding service base URL; improved documentation for embedding model selection and networking.
• Added an Ansible task to reliably pull the embedding model (nomic-embed-text) into the Ollama Embeddings instance before ExApp registration, ensuring the model is present and ready for use.

Networking and configuration fixes:

• Set the HP_EXAPPS_ADDRESS environment variable in the Docker Compose template to :::8780 to ensure ExApps are reachable via both IPv4 and IPv6, preventing connection issues when the backend resolves to an IPv6 address.