Closes#1864.
SECURITY.md was restored to main in #1843 but never added to v2/main.
Because v2/main is the develop branch merged into main at milestones, and
the two share no common git ancestor, the next milestone merge would
silently remove the security policy from the default branch a second time.
Copied byte-for-byte from main (sha256
bbc8aaa5a33d481f902c1b7ac260a4c9c0d41dac5bb2916607222dd205dda924,
2633 bytes). No content changes.
Claude-Session: https://claude.ai/code/session_01YAt8rqxysNbhYWLhoRm3fU
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
