Migrate better-result to 3.0

Treat the compiler as the migration ledger: inventory first, make mechanical changes, then resolve each remaining error by API branch.

1. Establish the migration surface

Read repository instructions, package manifests, lockfiles, TypeScript configuration, and validation commands. Verify that the source version is better-result 2.x and inspect the installed 3.0 declarations when available; package source outranks remembered APIs.

Search production code and tests for:

rg -n --glob '*.{ts,tsx,mts,cts}' \
  'TaggedError|Result\.(serialize|deserialize|hydrate|tryRecover|tryRecoverAsync|tryPromise|partition|gen)|matchError(Partial)?|TaggedErrorClass|Serialized(Result|Ok|Err)'

Classify every hit under the audited API changes in references/v3-api-diff.md. Include tests that structurally compare a Result containing a tagged error; tagged errors become iterable in v3 even though the Result.gen signature is unchanged. Record generated or vendored hits separately rather than editing them.

Complete when: the installed source version, target 3.0 API, validation commands, every matching production/test site, and every tagged-error Result assertion are accounted for by file and migration branch.