chore(release): bump framework and 8 skills to v3.1.0 (MINOR)

- Define immutable MAM_VERSION="3.1.0" runtime constant in lib.sh
- Bump YAML frontmatter version to 3.1.0 across all 8 skill packages
- Document v3.1.0 changelog, 2-tier TUI readiness architecture, and migration guide in VERSIONS.md
- Document new tuning knobs (MAM_KILL_ON_READY_TIMEOUT, MAM_DIALOG_TAIL_LINES, MAM_READY_EMPTY_GIVEUP) in .mam.env.example
- Add 3-way lockstep and immutability test suite in tests/test_version_consistency.py

.mam.env.example

@@ -158,6 +158,19 @@
 #default: 2
 # MAM_MAX_PANE_ROWS=2
 
+# Kill the session instead of preserving it when TUI readiness times out.
+#default: 0
+# MAM_KILL_ON_READY_TIMEOUT=0
+
+# Number of trailing non-blank pane lines scanned for blocking modal signatures.
+#default: 8
+# MAM_DIALOG_TAIL_LINES=8
+
+# Consecutive empty captures before wait_for_tui_ready declares the pane unobservable.
+# NOTE: distinct from SKS_EMPTY_GIVEUP, which governs send_keys_safe quiescence (default 3).
+#default: 5
+# MAM_READY_EMPTY_GIVEUP=5
+
 # ==============================================================================
 # deploy / distribution source (for forks/mirrors)
 # ==============================================================================