feature - 161 implement RFC 027 phase 1-3: groundwork and validation fixes

[dannymeijer]

Summary

This PR closes out RFC 027 phase 1-3 by landing the remaining compiler/tooling groundwork and folding in the regressions found during validation.

It adds the new registry-backed highlighting/generation plumbing, simplifies stdlib source-module routing around __incan_std, and fixes correctness issues in Rust interop field emission, Result constructor inference, explicit generic bound checking, and VS Code keyword highlighting. The goal is to leave the branch stable enough to merge before starting RFC 031.

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• CI / tooling
• RFC (adds/updates docs/RFCs/*)

Area(s)

Select the primary areas touched (used for review routing; labels are managed separately):

• Incan Language (syntax/semantics)
• Compiler (frontend/backend/codegen)
• Tooling (CLI/formatter/test runner)
• Editor integration (LSP/VS Code extension)
• Runtime / Core crates (stdlib/core/derive)
• Documentation

Key details

• User-facing behavior: assert now highlights as flow control rather than async syntax; Rust import field access like consts.PI now emits valid Rust path syntax; Ok(...) / Err(...) payload mismatches are reported correctly instead of being masked by the enclosing return type.
• Internals: keyword highlighting is now generated from canonical registry metadata in incan_core::lang; stdlib handling now consistently routes std.* modules through emitted crate::__incan_std::* source modules; typechecker call validation restores explicit generic-bound enforcement and generic constructor result typing.
• Risks: the biggest risk area is cross-layer drift between registry/typechecker/emitter/tooling behavior, especially around stdlib module routing and soft-keyword/editor metadata. This PR adds targeted regressions to reduce that risk.

Testing / verification

• make test / cargo test
• make examples (if relevant)
• incan fmt --check . (if relevant)
• Manual verification described below

Manual verification notes:

• Ran cargo test
• Ran cargo clippy --all-targets --all-features
• Ran mkdocs build --strict
• Ran cargo run --bin generate_vscode_grammar_keywords
• Verified targeted regressions for:
  • Rust import field access emission (consts.PI -> consts::PI)
  • TitleCase value-vs-type emission behavior
  • explicit generic bound failures
  • Ok(...) / Err(...) payload mismatch detection
  • VS Code keyword bucketing for assert

Docs impact

• No docs changes needed
• Docs updated
• Docs follow Divio intent (tutorial/how-to/reference/explanation) where applicable

If docs updated:

• Link(s): workspaces/docs-site/docs/RFCs/027_incan_vocab_crate.md, workspaces/docs-site/docs/RFCs/031_library_system_phase1.md, workspaces/docs-site/docs/RFCs/034_incan_pub_registry.md, workspaces/docs-site/docs/contributing/explanation/architecture.md, workspaces/docs-site/docs/contributing/how-to/extending_language.md, workspaces/docs-site/docs/release_notes/0_2.md, editors/vscode/README.md

Checklist

• I kept public docs user-focused and moved internals to contributing docs when appropriate
• I avoided duplicating canonical install/run instructions in multiple places
• I added/updated tests where it materially reduces regressions