docs: update README, architecture, and demo docs for M15a revocation

Update test counts (525+ → 600+), table counts (17 → 18), endpoint
counts (68 → 70), add revocation/CRL endpoints to API overview, add
certificate_revocations table to schema docs, update M15 roadmap to
show M15a complete and M15b remaining.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/architecture.md

@@ -30,7 +30,7 @@ flowchart TB
     end
 
     subgraph "Data Store"
-        PG[("PostgreSQL 16\n17 tables\nTEXT primary keys")]
+        PG[("PostgreSQL 16\n18 tables\nTEXT primary keys")]
     end
 
     subgraph "Agent Fleet"

docs/demo-advanced.md

@@ -501,7 +501,7 @@ flowchart TB
     end
 
     subgraph "Data Store"
-        PG["PostgreSQL 16\n17 tables, TEXT PKs"]
+        PG["PostgreSQL 16\n18 tables, TEXT PKs"]
     end
 
     subgraph "Agent (certctl-agent)"