fix(headless): align the one-shot runner with the direct rosterless profile

The shipped headless profile is base + headless (the direct-core front
door), and its installation-owned migration rewrites the old three-bundle
tuple down to that template, so a one-shot run composes no preset roster.
The runner's optional preset composition was compensating in the wrong
direction: it re-added roster reads the shipped profile never satisfies,
and its golden pinned a header field only a roster-bearing deployment
produces. The runner, the headless bundle manifest, and the dsh-run golden
return to the direct shape; skills in a direct run flow through the base
host rows' global layer, which is what the repository-plugin e2e proves.

examples/headless-agent/tests/snapshots/dsh-run/session.expected.jsonl

@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0,"agentPreset":"standard"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"permission/preset","seq":0,"time":0,"data":{"preset":"danger-full-access"}}
 {"type":"sandbox/mode","seq":1,"time":0,"data":{"mode":"danger-full-access"}}
 {"type":"approval/policy","seq":2,"time":0,"data":{"policy":"never"}}