feat: TypeScript SDK (agentlens-sdk) and OpenCode plugin (opencode-agentlens)

- packages/sdk-ts: BatchTransport, TraceBuilder, models, decision helpers
  Zero external deps, native fetch, ESM+CJS output
- packages/opencode-plugin: OpenCode plugin with hooks for:
  - Session lifecycle (create/idle/error/delete/diff)
  - Tool execution capture (before/after -> TOOL_CALL spans + TOOL_SELECTION decisions)
  - LLM call tracking (chat.message -> LLM_CALL spans with model/provider)
  - Permission flow (permission.ask -> ESCALATION decisions)
  - File edit events
  - Model cost estimation (Claude, GPT-4o, o3-mini pricing)

packages/sdk-ts/src/decision.ts

@@ -0,0 +1,29 @@
+import type { DecisionPointPayload, DecisionType, JsonValue } from "./models.js";
+import { generateId, nowISO } from "./models.js";
+
+export interface CreateDecisionInput {
+  type: DecisionType;
+  chosen: JsonValue;
+  alternatives?: JsonValue[];
+  reasoning?: string;
+  contextSnapshot?: JsonValue;
+  durationMs?: number;
+  costUsd?: number;
+  parentSpanId?: string;
+  timestamp?: string;
+}
+
+export function createDecision(input: CreateDecisionInput): DecisionPointPayload {
+  return {
+    id: generateId(),
+    type: input.type,
+    chosen: input.chosen,
+    alternatives: input.alternatives ?? [],
+    reasoning: input.reasoning,
+    contextSnapshot: input.contextSnapshot,
+    durationMs: input.durationMs,
+    costUsd: input.costUsd,
+    parentSpanId: input.parentSpanId,
+    timestamp: input.timestamp ?? nowISO(),
+  };
+}