Set up and seed the GitHub Wiki

[wimaan3]

Context

Enable + seed the Wiki as the navigable user/contributor knowledge base.

Acceptance criteria

• Wiki enabled.
• Pages: Home/overview, Quickstart (Windows), Vault format spec (frontmatter, structural tags, managed sections), Ports-&-Adapters guide, ADR index, Glossary.
• Linked from README.

[wimaan3]

Wiki pages + seed script merged (docs/wiki/ + scripts/seed-wiki.sh) and the wiki feature is enabled. One manual step remains — GitHub has no API to create the first wiki page: create it once at https://github.com/3MagicLabs/Grandplan/wiki, then run scripts/seed-wiki.sh to push all pages. Leaving open until the wiki is live.