#317 Use UUID-based Secret Identifiers with Descriptions

## Problem Currently secrets use human-readable paths like 'database/prod' or 'api/credentials'. This allows users to potentially guess or enumerate secret paths. ## Security Concern Human-readable names can be guessed, leading to accidental or intentional access. ## Solution Use UUID-based identifiers with human-readable descriptions: - secret_id: UUID (primary key, used in Vault path) - name: Human-readable name for UI display - description: What this secret is for - Vault path: highway/tenants/{tenant_id}/{uuid} ## Benefits - Secrets cannot be guessed/enumerated by name - Names can be changed without path changes - Better audit trail (immutable IDs) ## Trade-offs - Less intuitive for workflow authors - Requires lookup by name in workflow tools - Migration complexity for existing secrets ## Acceptance Criteria - New secrets created with UUID identifiers - API supports lookup by name or UUID - Migration tool for existing path-based secrets - Workflow tools support both UUID and name lookup