chore(synapse): replace Italian ImportError strings with English DX messages

[MarcoPorcellato]

Problem

synapse.py raises Italian ImportError messages:

LangChain non rilevato. Installa 'langchain-core' per usare Synapse.
LlamaIndex non rilevato. Installa 'llama-index' per usare Synapse.

KINETIC already uses English optional-dependency hints (uv sync --extra ai). Mixed language breaks consistency and operator UX.

Clean Architecture lens

Aspect	Assessment
Ring	Interface Adapter (SYNAPSE)
Uncle Bob	Clean Code: ubiquitous language — English for operator-facing errors

Proposed Solution

Mirror KINETIC wording:

Missing AI export dependencies. Install with: uv sync --extra ai

Files

• src/logseq_matryca_parser/synapse.py
• tests/test_synapse.py (assert message substring if tested)

Definition of Done

• English messages aligned with kinetic.py
• make all passes