feat(transform): name rebinding in SchemaRouter (repoint references at a different object)

[pyramation]

Summary

SchemaRouter object routes can now rebind — repoint a reference at a different object, not just a different schema. Routing preserves identity (same function, new address); rebinding is the substitution primitive: satisfy a reference's contract with another implementation.

An object route target is now string | ObjectRoute, where the shorthand string keeps today's meaning exactly:

interface ObjectRoute {
  schema?: string | null;  // null = de-qualify (rely on search_path)
  name?: string;           // rebind to a different object name
}

new SchemaRouter({
  accounts: {
    functions: { current_actor: { schema: null, name: 'current_user_id' } },
    relations: { members: { schema: 'app', name: 'users' } }
  }
});
// accounts.current_actor()              -> current_user_id()
// REFERENCES accounts.members(id)       -> REFERENCES app.users(id)

• New resolveObject(schema, name, ns): ObjectRoute | undefined is the full-fidelity resolver; resolve() now delegates to it and keeps its exact schema-only semantics (a null/name-only target reads as "unchanged" there), so every existing caller behaves identically.
• A rebind naming no schema inherits the route's schema-level default; schema: null de-qualifies, matching the ExtensionRouter to: null convention.
• transformNameList / transformRelation apply { schema, name } targets, covering call sites in expressions, defaults, policies, FK target tables (RangeVar), DROP/COMMENT object lists, and references inside LANGUAGE sql and PL/pgSQL bodies (via the existing AST body walk).
• New introspection: hasNameRebinds() (rebinds are inexpressible by the string-level passes, so callers must take the AST path) and nameRebinds() for reporting/verification by consumers.

Tests: 9 new cases (unit resolution + call-site/FK/policy/sql-body/de-qualify/sibling-isolation through transformSqlStatement); full @pgsql/transform suite green (8 suites / 228 tests).

Link to Devin session: https://app.devin.ai/sessions/025fb88043964fdbb335ac5e39df2478
Requested by: @pyramation

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