feat(analyzer): add phase-1 structured skill summaries

[rodboev]

Summary

SkillSpector currently scans AISOP/AISP bundles as generic directories and never says that a structured workflow format was found or which workflow roles were present. This phase-1 slice teaches recursive discovery and build-context to recognize valid *.aisop.json bundles, then emits one LOW informational summary finding without changing scoring or existing rule behavior.

Refs #130

This follows the phased implementation sketch and AISOP/AISP bundle examples in #130.

Root cause

src/skillspector/multi_skill.py only recognizes root SKILL.md layouts or immediate subdirectories that contain SKILL.md or skill.md, so --recursive misses structured subdirectories that are expressed only through valid AISOP/AISP bundle files. src/skillspector/nodes/build_context.py builds generic scan context and never classifies those bundles, while src/skillspector/nodes/analyzers/__init__.py has no structured-skill analyzer in the registry-driven graph. The bundle parser also needed to follow the issue schema itself, with workflow nodes at user.content.functions and constraint strings in functions.*.constraints, rather than an invented nested aisop.functions shape. The result is simple: valid structured bundles can be scanned, but the report has no structured-skill summary surface at all.

Diff Notes

• Add src/skillspector/structured_skill.py as the shared detector for valid *.aisop.json AISOP/AISP bundles and their summarized metadata, reading workflow nodes from user.content.functions and AISP resources from user.content.aisp_contract.resources.
• Reuse that detector in src/skillspector/multi_skill.py so --recursive can treat immediate structured subdirectories as skills while preserving root SKILL.md precedence.
• Populate structured_skill_context in src/skillspector/nodes/build_context.py and src/skillspector/state.py without changing the public report schema.
• Add src/skillspector/nodes/analyzers/structured_skill_roles.py and register it in src/skillspector/nodes/analyzers/__init__.py so the graph emits one LOW SSR-1 structured summary finding.
• Add focused coverage in tests/test_multi_skill.py, tests/nodes/test_build_context.py, tests/nodes/analyzers/test_registry.py, tests/nodes/analyzers/test_structured_skill_roles.py, and tests/unit/test_cli.py.

Scope

• Phase 1 only. This PR detects valid AISOP/AISP bundles and summarizes them with one additive LOW finding.
• No severity adjustments, no meta_analyzer changes, and no changes to existing static, behavioral, MCP, or semantic findings.
• No report-schema additions beyond the existing Finding fields.
• No Pi extension changes in extensions/skillspector.ts.
• No full role-aware score downgrades, no malformed-bundle warning surface, and no claim of complete AISOP/AISP spec coverage.

Verification

• python -m pytest tests/test_multi_skill.py tests/nodes/test_build_context.py tests/nodes/analyzers/test_registry.py tests/nodes/analyzers/test_structured_skill_roles.py tests/unit/test_cli.py -q - pass, 46 passed, 1 warning
• uv run ruff check src/ tests/ - pass
• uv run ruff format --check src/ tests/ - pass
• CI Lint & Test (Python 3.12), Lint & Test (Python 3.13), and DCO Check - pending maintainer approval if fork checks are gated

Notes

• This slice stops at detection and summary. Role-aware severity adjustments remain follow-up work on top of the new structured context.