fix(#2116): use resolvable paths in surface.md require + correct package name

Four require() examples in commands/gsd/surface.md used bare
'gsd-core/...' specifiers that Node cannot resolve (wrong package
name + runtime-mirror layout off module path). Now derives the path
from runtimeConfigDir. Also fixes reinstall hint from
'npm i -g gsd-core' to 'npm i -g @opengsd/gsd-core'.

tests/fixtures/golden-install-parity/opencode.json

@@ -95,7 +95,7 @@
   "command/gsd-spec-phase.md": "b92bca076ca2c5c6",
   "command/gsd-spike.md": "1b2fa4b468e831dc",
   "command/gsd-stats.md": "51af934859f87623",
-  "command/gsd-surface.md": "26a5f0aab82c1c4a",
+  "command/gsd-surface.md": "e559ca6733ce288f",
   "command/gsd-thread.md": "ae3b000bee0ee1e0",
   "command/gsd-ui-phase.md": "21c9c043d813dc0a",
   "command/gsd-ui-review.md": "ef36603b519e8fe8",
@@ -485,7 +485,7 @@
   "skills/gsd-spec-phase/SKILL.md": "332028ed34b85b1f",
   "skills/gsd-spike/SKILL.md": "9303cd74a8bf0741",
   "skills/gsd-stats/SKILL.md": "2af976632e239069",
-  "skills/gsd-surface/SKILL.md": "ea512089d0e1d057",
+  "skills/gsd-surface/SKILL.md": "a0cec79a0bbf9c97",
   "skills/gsd-thread/SKILL.md": "9ff9979a8213dbf8",
   "skills/gsd-ui-phase/SKILL.md": "5eee1bdd13640252",
   "skills/gsd-ui-review/SKILL.md": "c99d6725326bfbc4",