* feat(envvars): add LARKSUITE_CLI_AGENT_NAME accessor
envvars.AgentName() reads LARKSUITE_CLI_AGENT_NAME so business code can identify the agent driving the CLI. Value is sanitised (trim, reject control chars, 128-byte cap) and returns "" when unset or invalid. Local-only; not sent to the server.
* refactor(envvars): consolidate agent env accessors, dedupe sanitize
Move agent-trace reading from cmdutil.AgentTraceValue into envvars.AgentTrace(), symmetric with AgentName and sharing one sanitizeSingleLine. secheader.go now only assembles headers (BaseSecurityHeaders calls envvars.AgentTrace()); the duplicated sanitize and its os/unicode imports are gone. The X-Agent-Trace header and its behaviour are unchanged.
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Co-authored-by: liangshuo-1 <266696938+liangshuo-1@users.noreply.github.com>