release: v0.5.0 Fine Sift

[nullhack]

Summary

• Subflow exit resolution: exit names now resolve through parent transition map instead of being used directly as state IDs
• Subflow chaining: atomic exit + re-enter next subflow (e.g., discovery-flow → architecture-flow)
• Recursive subflow entry: handles 3-level nesting (main-flow → feature-dev-flow → planning-flow)
• JSON-first output: --json replaced with --text; JSON is now the default CLI output
• next shows all transitions: includes blocked/guarded with trigger→target, status, and condition hints
• states --session and validate --session: session-aware variants for current (sub)flow
• check --session <trigger>: fixed argparse consuming target as flow_file

Bug Fixes

• resolve_subflows() .yaml extension fallback for flow references without extension
• Stack frame records correct parent state (subflow wrapper, not pre-transition state)
• session init auto-enters subflow when first state has flow: field

Test Plan

• 292 tests pass (176 unit + 116 feature), 4 skipped
• ruff check . clean
• ruff format --check . clean
• Full dry run of TDD-review cycle with JSON output verified