Feature Flags & CLI Toggles — adaptive, intelligent gates, NL parser

[DevVig]

Summary
Introduce explicit feature flags and CLI toggles for adaptive orchestration, intelligent gates, and natural language parsing. Provide env + CLI controls and document behavior.

Why

• Make enhancements opt-in and controllable per project
• Support strict mode/deterministic runs on demand

Scope

• Flags in .a2dev/ config + environment + CLI args

Tasks

• Add flags: A2DEV_ADAPTIVE, A2DEV_INTEL_GATES, A2DEV_NL_PARSER
• Map to CLI options: --adaptive, --intelligent-gates, --nl-parser
• Persist defaults in .a2dev/intelligence.yaml and .a2dev/perf.yaml
• Display effective modes in CLI greetings and status summaries
• Document flags in README_A2Dev.md

Acceptance Criteria

• Flags visible via CLI and effective modes printed on start
• All new features disabled by default; enabling each shows expected behavior

References

• suggestion.md (Feature flag guidance implied for adaptive/gates)
• a2a/core/__init__.py, a2a/cli.py