feat(ai): session harness contract — incomplete, run_id, confirm bind

Add docs/16 for session state machine, incomplete/resume, queue semantics,
and agent-loop/harness/MCP gap review. Wire RunOutcome on max-rounds,
run_id through audit, TrimMessages/Redact hooks, ConfirmBindHash on write
confirm path; session file skeleton without HTTP yet. No push.

server/internal/ai/outcome.go

@@ -0,0 +1,19 @@
+package ai
+
+// RunOutcome 单次 Agent 运行结束状态（对齐 aiops docs/ai-agent/13）。
+const (
+	OutcomeCompleted       = "completed"
+	OutcomeIncomplete      = "incomplete"
+	OutcomeFailed          = "failed"
+	OutcomeCancelled       = "cancelled"
+	OutcomeAwaitingConfirm = "awaiting_confirm"
+)
+
+// IncompleteReason 仅当 Outcome==incomplete 时有意义。
+const (
+	ReasonMaxSteps       = "max_steps"
+	ReasonContextBudget  = "context_budget"
+	ReasonToolTimeout    = "tool_timeout"
+	ReasonLLMTimeout     = "llm_timeout"
+	ReasonSafetyAbort    = "safety_abort"
+)