Add taxonomy-driven semantic link discovery and storage

[jimador]

Summary

Adds an experimental taxonomy layer for propositions and an end-to-end semantic-link pipeline:

• validated taxonomy model, classifier, decoration pass, and taxonomy query API
• ontological semantic-link discovery
• in-memory SemanticLinkStore SPI and durable Drivine/Neo4j implementation
• focused unit and integration coverage across the new APIs

All newly introduced public APIs are marked @ApiStatus.Experimental.

Why

This provides the reusable Dice-side foundation for classifying accumulated memories, discovering connections through shared taxonomy ancestry, and persisting reviewable semantic-link candidates.

Validation

• Full seven-module Maven reactor: BUILD SUCCESS
• Dice Report tests: 31 passed
• Dice integration tests: 12 passed
• Each logical packet was independently exercised against the me application before consolidation
• Final aggregate branch matches the reviewed packet snapshots exactly

Database impact

The durable store lazily creates :SemanticLink nodes when callers record candidates. No manual migration or backfill is required.