Add project-specific AI agent guidance files that work across
Claude Code, Codex, and Gemini CLI. Includes 5 critical rules
(sta/ protection, clang-format exclusions, DCO compliance,
submodule hygiene, upstream bug tracing) and 4 sub-guides
for build, testing, CI, and coding patterns.
Relocate triage-issue skill to .agents/skills/ (cross-tool)
with .claude/skills symlink for backwards compatibility.
Add .gemini/commands/triage-issue.toml for Gemini CLI support.
Signed-off-by: Jaehyun Kim <jhkim@precisioninno.com>