Propose Swift typed tooling lane

[SoundBlaster]

Summary

• What changed? Added Proposal 0050 for a Swift typed tooling lane over SpecGraph artifacts.
• Link related issue/task (if any): operator discussion about using Swift as a pragmatic second implementation language.

Motivation

• Why is this change needed? Swift adoption needs an explicit boundary so it does not become an accidental Python supervisor rewrite or duplicate write-authority layer.
• What problem, gap, or user need does it address? Defines Swift as an optional read-only typed tooling/SDK lane for artifact clients, validators, and future SpecSpace/native consumers.

Goals

• What should this PR achieve? Capture the proposal, source draft, promotion trace, and regression coverage for Proposal 0050.
• What is intentionally out of scope? No Swift code, no supervisor rewrite, and no canonical write authority for Swift tooling.

Changes

• Added docs/proposals/0050_swift_typed_tooling_lane.md.
• Added source draft docs/archive/proposal_sources/0050_swift_typed_tooling_lane.md.
• Added Proposal 0050 to tools/proposal_promotion_registry.json.
• Extended promotion trace regression coverage for Proposal 0050.

Validation

• Tests added/updated for changed behavior
• Local checks passed

Commands run:

python3 -m pytest -q tests/test_supervisor.py -k 'proposal_promotion_trace or proposal_promotion_index'
git diff --check
make proposal-spec-trace

Results:

• Promotion trace/index tests: 51 passed, 559 deselected.
• make proposal-spec-trace: entry_count = 50.
• Pre-commit hooks passed during commit.

Risks / Notes

• Backward compatibility impact: none; proposal and registry metadata only.
• Migration/config changes required: none.
• Known limitations: first Swift runtime/tooling slice remains follow-up work.

Checklist

• PR title clearly describes the change
• Scope is focused and minimal
• Documentation updated (or N/A)
• No secrets or sensitive data added