chore: repoint URLs to Nimblesite/osprey after org move

[MelbourneDeveloper]

TLDR

Repoint every MelbourneDeveloper/osprey URL to Nimblesite/osprey after the org transfer.

Details

The repo moved from MelbourneDeveloper/osprey into the Nimblesite org. This updates all 24 files that hard-coded the old path:

• Website — index.html, _data/navigation.json, _data/site.json (sameAs), disclaimer.md, status.md, js/main.js, scripts/copy-spec.js, the spec/* pages, and the blog posts.
• READMEs / docs — README.md, vscode-extension/README.md (incl. the raw-githubusercontent logo URL), CONTRIBUTING.md, docs/RELEASING.md, docs/specs/0020.
• Package metadata — Cargo.toml repository, vscode-extension/package.json (repo + bugs), tree-sitter-osprey/{package.json,tree-sitter.json}, shipwright.json (repository + repo).
• Release pipeline — release.yml PRODUCT_REPO (drives the brew/scoop download URLs) and the Entra-OIDC subject comment.

Intentionally NOT changed:

• compiler/examples/tui/api_browser.osp — "MelbourneDeveloper" there is live-API sample data (the GitHub username the TUI demo lists repos for), not a repo link. Changing it would alter the tested example's output.
• homebrew-package/* — explicitly labelled Legacy / local-dev only; its banner already points to Nimblesite/homebrew-tap as the official tap.

How Do The Automated Tests Prove It Works?

• git grep "MelbourneDeveloper/osprey" returns zero matches after the change.
• All six edited JSON files (shipwright.json, both package.json, tree-sitter.json, navigation.json, site.json) parse as valid JSON.
• npm run test:shipwright → shipwright.json: valid (the repo field change passes the manifest validator that CI also runs).
• CI's changes filter sees non-website files, so the full Rust/build/test gate runs; these are string/metadata-only edits with no logic impact.

⚠️ Follow-up (not in this PR): the Marketplace publish uses Entra-ID OIDC with subject repo:Nimblesite/osprey:environment:release. The Azure federated credential must be updated to trust the new Nimblesite/osprey subject (or switch that job to the org VSCODE_MARKETPLACE_PAT, like Basilisk), or the next release's Marketplace leg will fail.