Cleanup: Archive versioned architecture docs

[rgfaber]

Problem

We have architecture docs with version prefixes that are outdated:

• architecture/v0.8.0-OVERVIEW.md
• architecture/v0.8.0-CHANGELOG.md
• architecture/v0.8.0-ROADMAP.md

We're now at v0.14.0. This creates confusion.

Solution

1. Move versioned docs to architecture/archive/
2. Create version-agnostic architecture/OVERVIEW.md (always current)
3. Keep ROADMAP.md in root - describes vision, not tied to version
4. Use CHANGELOG.md for release history

Files to Archive

• architecture/v0.8.0-OVERVIEW.md → architecture/archive/
• architecture/v0.8.0-CHANGELOG.md → architecture/archive/
• architecture/v0.8.0-ROADMAP.md → delete (redundant with ROADMAP.md)

Context

Documentation hygiene - no more versioned architecture docs that get stale.