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.

Cargo.lock

@@ -37,7 +37,7 @@ dependencies = [
  "derive_more",
  "encoding_rs",
  "flate2",
- "foldhash",
+ "foldhash 0.2.0",
  "futures-core",
  "h2 0.3.27",
  "http 0.2.12",
@@ -152,7 +152,7 @@ dependencies = [
  "cookie",
  "derive_more",
  "encoding_rs",
- "foldhash",
+ "foldhash 0.2.0",
  "futures-core",
  "futures-util",
  "impl-more",
@@ -614,6 +614,16 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
 
+[[package]]
+name = "combine"
+version = "4.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cfc320937d09e6de266b31b9afb480f197d7a861be86be7cb2ea7e5d1bfffc5e"
+dependencies = [
+ "bytes",
+ "memchr",
+]
+
 [[package]]
 name = "console"
 version = "0.16.4"
@@ -1103,6 +1113,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "foldhash"
 version = "0.2.0"
@@ -1343,6 +1359,17 @@ dependencies = [
  "allocator-api2",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash 0.1.5",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.17.1"
@@ -1919,6 +1946,15 @@ version = "0.4.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f9f8bd3e56ce4dfc153cf470fffbfa98c7620958b312ca5c3a4b8d5181fd13c6"
 
+[[package]]
+name = "lru"
+version = "0.12.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "234cf4f4a04dc1f57e24b96cc0cd600cf2af460d4161ac5ecdd0af8e1f3b2a38"
+dependencies = [
+ "hashbrown 0.15.5",
+]
+
 [[package]]
 name = "macro_rules_attribute"
 version = "0.1.3"
@@ -1987,12 +2023,14 @@ dependencies = [
  "clap",
  "futures",
  "jsonwebtoken",
+ "lru",
  "mem-chunk",
  "mem-core",
  "mem-ingest",
  "mem-llm",
  "mem-store",
  "pgvector",
+ "redis",
  "reqwest",
  "serde",
  "serde_json",
@@ -2040,6 +2078,7 @@ dependencies = [
  "futures",
  "mem-chunk",
  "mem-core",
+ "regex",
  "serde",
  "serde_json",
  "serde_yaml",
@@ -2709,6 +2748,21 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "redis"
+version = "0.25.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e46922bd01fefcfdcf58d9cd626da082bb2cde27211920dacfde6b2ecf9a35b"
+dependencies = [
+ "combine",
+ "itoa",
+ "percent-encoding",
+ "ryu",
+ "sha1_smol",
+ "socket2 0.5.10",
+ "url",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.5.18"
@@ -3079,6 +3133,12 @@ dependencies = [
  "digest 0.11.3",
 ]
 
+[[package]]
+name = "sha1_smol"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbfa15b3dddfee50a0fff136974b3e1bde555604ba463834a7eb7deb6417705d"
+
 [[package]]
 name = "sha2"
 version = "0.10.9"