Roll the autonomy-modes system into agentic-skeleton for all workspaces #2

Port the FireDrill prototype (v0.127.0, ff5dd9d): VIBE workflow.autonomy default_mode/cap; autonomy-intent.sh UserPromptSubmit classifier; continuation-counter stop-gate replacing the one-and-done bail; .autonomy-state gitignore. Follow-ups: ADR; vibe-yaml-schema + greenfield defaults; deprecate workflow.default_autonomy_mode; decide the ambiguous→off default.