refactor(#2384): leaf dispatch table + runCommand collapse (ADR-2346 P4) (#2392)

* refactor(#2384): leaf dispatch table + runCommand collapse (ADR-2346 P4)

Cutover all 55 remaining case arms from runCommand's switch to
HOST_COMMAND_ROUTERS. runCommand now contains only its default case
(~40 lines): the three-layer dispatch (capability → overlay → host table)
plus the unknown-command diagnostic. The 73-case switch is dissolved.

Each case body was relocated verbatim to a module-scope route*Command
function via a brace-matching extractor; inner break; statements (from
_dispatchNonFamily early-exit patterns) were converted to return;
(5 arms affected); loop break; statements preserved.

Closes #2384

* chore: retrigger CI

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

@@ -110,7 +110,7 @@
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",
   "gsd-core/bin/ensure-runtime-build.cjs": "51bc64467ab30f62",
-  "gsd-core/bin/gsd-tools.cjs": "48b736dd16863746",
+  "gsd-core/bin/gsd-tools.cjs": "cae92a5bde4f3414",
   "gsd-core/bin/gsd_run": "62d9b647ede212e6",
   "gsd-core/bin/shared/config-defaults.manifest.json": "517e6a7c1e9f4f16",
   "gsd-core/bin/shared/config-schema.manifest.json": "0109a5a9866a24e0",