refactor(httpapi-exercise): migrate query-schema-drift scenarios into harness

Move the 8 standalone scenarios from
packages/opencode/test/server/httpapi-query-schema-drift.test.ts into
the route-coverage exerciser as `.viaSdk(...)` scenarios. Each one
exercises a routing-aware GET through the real SDK client wired to the
in-process router, so the SDK's auto-injected `?directory=...` /
`?workspace=...` query params hit the same typed schemas as in production.

Routes now covered by `.viaSdk(...)` scenarios in the exerciser:
  /session                          (session.list.via_sdk)
  /session/{sessionID}/message      (session.messages.via_sdk)
  /find/file                        (find.files.via_sdk)
  /find                             (find.text.via_sdk)
  /file/content                     (file.read.via_sdk)
  /experimental/session             (experimental.session.list.via_sdk)
  /experimental/tool                (experimental.tool.list.via_sdk)
  /vcs/diff                         (vcs.diff.via_sdk)

Standalone httpapi-query-schema-drift.test.ts deleted — its coverage
now lives in the harness alongside every other route test, single
source of truth.

149/149 scenarios pass after migration (139 existing + 2 from
proof-of-concept #26604 + 8 migrated here).