chore(spec): regenerate the four reference pages both sides moved

The os-regen driver kept the branch side of content/docs/references/{data/field,
data/object, shared/value-domain, system/migration}.mdx in the merge of main
(2972097); main had re-derived their page descriptions. Regenerated with
gen:schema + gen:docs from the merged tree: main's derived descriptions plus
this branch's retired currencyConfig.precision rows. The resulting tree equals a
driverless merge-tree of main and the pre-merge tip (5431f62).

Claude-Session: https://claude.ai/code/session_01Rjy9MeetSfq34PKn81CRiN
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

content/docs/references/data/field.mdx

@@ -1,6 +1,6 @@
 ---
 title: Field
-description: Field protocol schemas
+description: "Field schemas of the ObjectStack Data Protocol: CurrencyConfig, CurrencyValue, Field and 7 more — each property with its type, default and a TypeScript example."
 ---
 
 {/* ⚠️  AUTO-GENERATED — DO NOT EDIT. Run build-docs.ts to regenerate. Hand-written docs live in the module folders under content/docs/. */}

content/docs/references/data/object.mdx

@@ -1,6 +1,6 @@
 ---
 title: Object
-description: Object protocol schemas
+description: "Object schemas of the ObjectStack Data Protocol: ApiMethod, ApiOperation, Index and 13 more — each property with its type, default and a TypeScript example."
 ---
 
 {/* ⚠️  AUTO-GENERATED — DO NOT EDIT. Run build-docs.ts to regenerate. Hand-written docs live in the module folders under content/docs/. */}

content/docs/references/shared/value-domain.mdx

@@ -1,6 +1,6 @@
 ---
 title: Value Domain
-description: Value Domain protocol schemas
+description: "Standard value domains: one closed vocabulary and one membership predicate for settings and fields."
 ---
 
 {/* ⚠️  AUTO-GENERATED — DO NOT EDIT. Run build-docs.ts to regenerate. Hand-written docs live in the module folders under content/docs/. */}

content/docs/references/system/migration.mdx

@@ -1,6 +1,6 @@
 ---
 title: Migration
-description: Migration protocol schemas
+description: "Migration protocol — the two kinds of migration, kept apart on purpose."
 ---
 
 {/* ⚠️  AUTO-GENERATED — DO NOT EDIT. Run build-docs.ts to regenerate. Hand-written docs live in the module folders under content/docs/. */}