docs(spec): name the real chain entrypoint in the ADR-0087 entry

The semantic entry for the metric-family refusal told readers that
`applyMigrationChain` maps `step.semantic` onto the result. No such symbol
exists in the tree; the function is `applyMetaMigrations`
(packages/spec/src/migrations/chain.ts:68), which is what the CLI calls and
what the root api-surface exports.

The behaviour the sentence describes is correct — chain.ts:102 maps
`step.semantic` straight through with no per-document interpolation — so only
the identifier moves. It matters because this text ships in the migration
ledger and is printed by `os migrate meta` at protocol 18, where a reader who
greps the name finds nothing.

registry.ts is regenerated by `gen:migration-registry`, never edited by hand.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JbZnqu8bt6YqfJsr9vaFb3

Author: claude

packages/spec/src/migrations/entries/semantic/18.dashboard-widget-metric-family-multi-measure-refused.ts

@@ -58,7 +58,7 @@ export const entry: SemanticMigration = {
     + 'measures on a `metric` and the author meets the refusal later, at publish. ⇒ Do not '
     + 'read a green editor as a clean dashboard; re-parse through the spec. '
     + '⚠️ AND THE TODO CANNOT NAME YOUR MEASURES: a `SemanticMigration` is static prose '
-    + 'emitted once per hop — `applyMigrationChain` maps `step.semantic` straight onto the '
+    + 'emitted once per hop — `applyMetaMigrations` maps `step.semantic` straight onto the '
     + 'result with no per-document interpolation and no filtering by whether the stack '
     + 'even carries the shape — so `os migrate meta` prints THIS paragraph, not a list of '
     + 'your dropped measures. The refusal is what names them, per widget, on the re-parse. '

packages/spec/src/migrations/registry.ts

@@ -6762,7 +6762,7 @@ const step18: MigrationStep = {
         + 'measures on a `metric` and the author meets the refusal later, at publish. ⇒ Do not '
         + 'read a green editor as a clean dashboard; re-parse through the spec. '
         + '⚠️ AND THE TODO CANNOT NAME YOUR MEASURES: a `SemanticMigration` is static prose '
-        + 'emitted once per hop — `applyMigrationChain` maps `step.semantic` straight onto the '
+        + 'emitted once per hop — `applyMetaMigrations` maps `step.semantic` straight onto the '
         + 'result with no per-document interpolation and no filtering by whether the stack '
         + 'even carries the shape — so `os migrate meta` prints THIS paragraph, not a list of '
         + 'your dropped measures. The refusal is what names them, per widget, on the re-parse. '