test(web): keyless e2e — OTLP collector receives the session ledger

Boot the real dsh web tree against an in-test OTLP/HTTP collector and a
mock LLM server, drive one turn over /api, then SIGINT. Asserts the wire:
OTLP JSON structure and resource identity, both instrumentation scopes,
ledger event coverage in seq order, prompt fidelity in the exported body,
the first-of-step chunk projection, and the ops shutdown marker arriving
through the exit drain.

pnpm-lock.yaml

@@ -442,9 +442,15 @@ importers:
         specifier: ^4.2.0
         version: 4.2.0
     devDependencies:
+      '@deepseek-ai/dsh-llm-mock-server':
+        specifier: workspace:^
+        version: link:../../packages/support/llm-mock-server
       '@types/js-yaml':
         specifier: ^4.0.9
         version: 4.0.9
+      execa:
+        specifier: ^10.0.0
+        version: 10.0.0
       node-pty:
         specifier: 1.1.0
         version: 1.1.0(patch_hash=7a0c04f1f49d798a9ffe2f7f414c01064a44ca2489772d0c3e1235ab336755e6)