v13.0

v13.0 Language Completeness

Delivered: Rounded out the language with multi-line pipes, type aliases, TryFrom/TryInto traits, Map.collect string keys, native json { } object literals, VS Code extension v0.3.0, and complete documentation.

Key accomplishments:
- Multi-line pipe continuation: |> at end-of-line or start-of-continuation
- Type aliases: type Url = String and pub type UserId = Int with cross-module export
- TryFrom/TryInto: fallible conversions with auto-derived TryInto and ? operator support
- Map.collect string keys: Iter.zip dispatch fix for Map<String,V> collection
- Native json { } object literals: full compiler pipeline, 70 mesher usages migrated
- VS Code extension v0.3.0: m10-m13 grammar, json/type-alias snippets, packaged VSIX

See .planning/MILESTONES.md for full details.