Fix HTTP transport to apply the full middleware chain (tool filtering,
field validation, write audit logging, session recording) by extracting
shared execute_tool() from call_tool(). HTTP tools/list now respects
LM_ENABLED_TOOLS and LM_DISABLED_TOOLS filtering.

Cache LMConfig as singleton to avoid redundant env parsing per tool call.
Remove dead logging infrastructure (LogLevel, LogEvent, 7 event factories).
Update SECURITY.md, CHANGELOG.md, CONTRIBUTING.md for accuracy.