refactor(cli): remove generated /admin console shell from site generator

[rrrodzilla]

Summary

The runtime-dynamic admin console (the old /admin/* shell — schema catalog, generic CRUD, user management) moves to the standalone schemaforge-console repo, where it ships as versioned packages so a fix reaches every operator via a bump instead of a regenerate-and-redeploy. The CLI's site generate command stays and still emits the /app/* typed scaffold, the login page, the accessibility page, and the generated client.

Scope was deliberately narrow: remove only the /admin/* shell, keep everything /app/*. No backend changes — serve/bootstrap-admin/--admin-user seed the initial auth user, never served the console UI.

Changes

• Delete templates/site/src/admin/ (9 jinja files) and the ADMIN_TEMPLATES const + emit loop in commands/site/mod.rs.
• Relocate the helpers the kept /app shell still needs out of the deleted admin client into generated/api-client.ts.jinja: listSchemas, isSystemSchema, a minimal SchemaResponse/ListSchemasResponse (the sidebar nav stays runtime read-access-filtered, not a static list), and getMeta/MetaResponse (login branding).
• Rewire App.tsx: drop the Admin sidebar section, the admin-permissions query, the AdminLayout import and the /admin/* route; repoint the home, tenant-switch, and search redirects to `/app/${defaultEntity}` (already exported by the route manifest).
• Point login.tsx at the generated client; tidy stale admin wording in route-manifest, accessibility, and auth.ts.
• Tests: site_generate.rs now asserts no src/admin/ is emitted and the home redirect targets /app/; site_e2e smoke + a11y specs repointed to /app/* (the /app scaffold has no delete or user-management UI — those moved to the console).
• Docs: docs/site-guide.md, README.md, Taskfile.yml admin-console references dropped with a pointer to schemaforge-console; fixed a broken See also link and a stale index.html page-title claim.

Verification

• cargo nextest run -p schema-forge-cli — 334/334 pass (including the rewritten generator assertions)
• cargo clippy -p schema-forge-cli --all-targets — clean
• Regenerated site/ from the demo schemas: no src/admin/ dir, zero @/admin / /admin references, all relocated helpers present, login + App.tsx rewired
• tsc build resolves every relocation and redirect in this change

Pre-existing issues (NOT addressed here, unrelated to this change)

1. Workspace cargo fmt drift — rustfmt 1.8.0 reports 63 CLI-crate diffs in files this PR never touches (e.g. cli.rs). Deliberately not folded in to keep this diff focused.
2. tsc error in the generated site — App.tsx's <Toaster toastOptions={{ ariaLive }}> is invalid for the installed sonner version (present in main too). Left alone because it sits in the WCAG 4.1.3 a11y-rationale block.