Fix TypeBox schema consistency and add TypeBox patterns research

- schemas.md: Replace interface ResolvedTaskAttributes with TypeBox schema
  + Static<typeof> derivation (was the only raw interface in the doc set)
- schemas.md: Add explicit TypeBox naming convention table and pattern guide
- schemas.md: Use Nullable() helper for TaskInput optional categorical fields
  that can be explicitly set to null in YAML
- schemas.md: Reference typebox-patterns.md research for full analysis
- api-surface.md: Add note about Static<typeof> pattern consistency
- errors-validation.md: Use Value.Errors() for structured validation instead
  of bare Value.Check()
- New: docs/research/typebox-patterns.md — comprehensive TypeBox pattern
  evaluation covering Static, Values, Convert, Pointer, TemplateLiteral,
  generics, defaults, and concrete schema recommendations

docs/architecture/api-surface.md

@@ -107,7 +107,7 @@ function calculateTaskEv(p: number, scopeCost: number, impactWeight: number, con
 
 ## Return Types
 
-All return types are defined as TypeBox schemas (for runtime validation + JSON Schema export) with corresponding static TypeScript types.
+All return types are defined as TypeBox schemas (for runtime validation + JSON Schema export). The corresponding TypeScript types are derived via `Static<typeof Schema>` — no separate `interface` or `type` definitions. See [schemas.md](schemas.md) for the full naming convention.
 
 ### RiskPathResult