feat: Add Promotion-Time Attestations for Stella Ops

- Introduced a new document for promotion-time attestations, detailing the purpose, predicate schema, producer workflow, verification flow, APIs, and security considerations.
- Implemented the `stella.ops/promotion@v1` predicate schema to capture promotion evidence including image digest, SBOM/VEX artifacts, and Rekor proof.
- Defined producer responsibilities and workflows for CLI orchestration, signer responsibilities, and Export Center integration.
- Added verification steps for auditors to validate promotion attestations offline.

feat: Create Symbol Manifest v1 Specification

- Developed a specification for Symbol Manifest v1 to provide a deterministic format for publishing debug symbols and source maps.
- Defined the manifest structure, including schema, entries, source maps, toolchain, and provenance.
- Outlined upload and verification processes, resolve APIs, runtime proxy, caching, and offline bundle generation.
- Included security considerations and related tasks for implementation.

chore: Add Ruby Analyzer with Git Sources

- Created a Gemfile and Gemfile.lock for Ruby analyzer with dependencies on git-gem, httparty, and path-gem.
- Implemented main application logic to utilize the defined gems and output their versions.
- Added expected JSON output for the Ruby analyzer to validate the integration of the new gems and their functionalities.
- Developed internal observation classes for Ruby packages, runtime edges, and capabilities, including serialization logic for observations.

test: Add tests for Ruby Analyzer

- Created test fixtures for Ruby analyzer, including Gemfile, Gemfile.lock, main application, and expected JSON output.
- Ensured that the tests validate the correct integration and functionality of the Ruby analyzer with the specified gems.

docs/modules/policy/README.md

@@ -23,6 +23,7 @@ Policy Engine compiles and evaluates Stella DSL policies deterministically, prod
 - Governance and scope mapping in ../../security/policy-governance.md.
 - Readiness briefs: ../policy/secret-leak-detection-readiness.md, ../policy/windows-package-readiness.md.
 - Readiness briefs: ../scanner/design/macos-analyzer.md, ../scanner/design/windows-analyzer.md, ../policy/secret-leak-detection-readiness.md, ../policy/windows-package-readiness.md.
+- Ruby capability predicates design: ./design/ruby-capability-predicates.md.
 
 ## Backlog references
 - DOCS-POLICY-20-001 … DOCS-POLICY-20-012 (completed baseline).