feat: add specification for external provider injection (Level 1)

Add comprehensive specification for deploy-time modularity enabling users to
inject custom and third-party provider implementations without rebuilding
distribution images.

Key components:
- Complete specification (spec.md) with 32 functional requirements, 5 NFRs
- Implementation plan (plan.md) with 7 development phases
- Task breakdown (tasks.md) with 110 tasks organized by user story
- Container startup sequence with mermaid diagram showing 5 runtime phases
- Security considerations and forward compatibility planning
- Constitution updates for git commit guidelines and DCO sign-off

Technical approach:
- Init container architecture for provider installation
- Config merge using extra-providers.yaml schema
- Forward compatible with future LlamaStack native support
- Comprehensive error handling and status reporting

Documentation:
- Preflight validation specification (lls-preflight-spec.md)
- Complete CRD structure with validation tags
- Detailed error message formats
- Provider image packaging contract

Constitution updates (v1.4):
- Git commit message conventions
- AI-assisted commit guidelines (Assisted-by trailer format)
- Commit sign-off requirement (DCO)
- Commit hygiene standards

Assisted-by: Claude Code
Signed-off-by: Roland Huß <rhuss@redhat.com>

Author: rhuss

.gitignore

@@ -34,3 +34,7 @@ catalog-item
 config/manifests/bases/llama-stack-k8s-operator.clusterserviceversion.yaml
 
 .DS_Store
+
+# SDD and Claude Code directories
+.claude
+.specify