chore: add kiro spec-driven tooling and steering docs

Add the Kiro-style agentic SDLC tooling used to drive this project: the
.opencode/skills/kiro-* skill set (discovery, spec init/requirements/design/
tasks, validation, implementation, review, steering), the .kiro/settings
templates, and AGENTS.md describing the workflow. Update the spec docs
(assessment/design/requirements/tasks) to current state.

Scope tests/test_opencode_skills.py to the project's own openultrasast-*
skills so the third-party kiro-* tooling (which uses a different frontmatter
convention) no longer breaks the frontmatter check.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

.opencode/skills/kiro-spec-design/rules/design-discovery-light.md

@@ -0,0 +1,49 @@
+# Light Discovery Process for Extensions
+
+## Objective
+Quickly analyze existing system and integration requirements for feature extensions.
+
+## Focused Discovery Steps
+
+### 1. Extension Point Analysis
+**Identify Integration Approach**:
+- Locate existing extension points or interfaces
+- Determine modification scope (files, components)
+- Check for existing patterns to follow
+- Identify backward compatibility requirements
+
+### 2. Dependency Check
+**Verify Compatibility**:
+- Check version compatibility of new dependencies
+- Validate API contracts haven't changed
+- Ensure no breaking changes in pipeline
+
+### 3. Quick Technology Verification
+**For New Libraries Only**:
+- Use WebSearch for official documentation
+- Verify basic usage patterns
+- Check for known compatibility issues
+- Confirm licensing compatibility
+- Record key findings in `research.md` (technology alignment section)
+
+### 4. Integration Risk Assessment
+**Quick Risk Check**:
+- Impact on existing functionality
+- Performance implications
+- Security considerations
+- Testing requirements
+
+## When to Escalate to Full Discovery
+Switch to full discovery if you find:
+- Significant architectural changes needed
+- Complex external service integrations
+- Security-sensitive implementations
+- Performance-critical components
+- Unknown or poorly documented dependencies
+
+## Output Requirements
+- Clear integration approach (note boundary impacts in `research.md`)
+- List of files/components to modify
+- New dependencies with versions
+- Integration risks and mitigations
+- Testing focus areas