v0.1.0

docs: add VERSION file (0.1.0) + consolidate CHANGELOG for the release

The library version is 0.1.0 — declared in [workspace.package] (inherited by
all crates) and amber-node's package.json, and not yet published. Record it in
a top-level VERSION file (single source for scripts/tooling).

Since 0.1.0 has never shipped, fold the [Unreleased] entries into [0.1.0] (the
first release will contain them) and date it 2026-05-25. Reconcile the Windows
note with Plans.md Phase 12: the CreateProcessW debug-pipe path is implemented
but unvalidated off-Windows, so 0.1.0 ships Unix-only with a clean Unsupported
error on Windows browser capture — stated as a known limitation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>