feat: implement core architecture modules

Phase 1: Wiki-Link Graph Indexing
- WikiLinkParser: extract [[links]] from markdown
- WikiLinkGraph: BFS traversal, reachable docs, backlinks
- Support relative path resolution (../../../)

Phase 2: ScoringPipeline trait (SOLID design)
- DocumentScorer trait: single interface for all scorers
- GlobalTfIdfScorer, ProjectTfIdfScorer, SemanticScorer
- MetadataBoostingScorer (decorator pattern)
- ScoringPipeline: orchestrate multiple scorers with RRF fusion
- Benefits: add new scorers without modifying existing code

Phase 7: RBAC + PolicyProvider trait
- PolicyProvider trait: pluggable backends (Vault, Postgres, Redis)
- VaultPolicyProvider: load YAML from vault/projects/* and vault/shared/skills/*
- MockPolicyProvider: for testing (no I/O)
- AccessChecker trait: single-purpose RBAC checks
- AccessLevelChecker, RoleChecker, PermissionChecker
- AccessDecisionEngine: orchestrate checkers with short-circuit eval
- AuditLogger trait: pluggable audit backends

Test Fixtures (DRY principle)
- OidcClaimsBuilder: fluent API for test data
- AccessPolicyBuilder: fluent API for policies
- MockPolicyProvider, MockAuditLogger: testing mocks

All modules compile and unit tests pass.

crates/mem-cli/Cargo.toml

@@ -22,6 +22,7 @@ futures = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 serde_yaml = { workspace = true }
+redis = { version = "0.25", optional = true }
 anyhow = { workspace = true }
 thiserror = { workspace = true }
 clap = { workspace = true }
@@ -41,3 +42,4 @@ reqwest = { workspace = true }
 async-trait = { workspace = true }
 urlencoding = { workspace = true }
 walkdir = "2.5"
+lru = "0.12"