spec: normalize requirement titles and headings to canonical form

spec/functional/FR-001-module-manifest-activates.md

@@ -6,7 +6,7 @@ relationships:
   - target: "ix://agent-ix/filament-core-service/FR-035"
     type: "implements"
 ---
-# [FR-001] Module manifest activates against filament-core
+# FR-001: Module manifest activates against filament-core
 
 ## Description
 

spec/integration/IT-001-manifest-activation-roundtrip.md

@@ -6,7 +6,7 @@ relationships:
   - target: "ix://agent-ix/spec-objects-security/FR-001"
     type: "verifies"
 ---
-# [IT-001] Manifest activation roundtrip
+# IT-001: Manifest activation roundtrip
 
 ## Objective
 

spec/stakeholder/StR-001-module-activation.md

@@ -3,7 +3,7 @@ id: StR-001
 title: "Tier-2 security + identity objects"
 type: StR
 ---
-# [StR-001] Tier-2 security + identity objects
+# StR-001: Tier-2 security + identity objects
 
 ## Stakeholder Need