chore(repo): remove Nx

[jgoux]

Summary

• remove the remaining Nx configuration, package metadata, inference plugin workspace, dependencies, cache ignores, and lockfile graph
• update current contributor guidance to use package scripts and root-owned Turbo tasks for execution and dependency inspection
• preserve the build, generation, quality, live, auxiliary, and test graphs established by the preceding Turborepo migrations

Context

PR #6343 merged while this change was in progress, so this branch was rebased onto the updated develop branch containing its final live and auxiliary task migration. Task execution is now owned entirely by package scripts and Turbo.

Affected execution, persistent cache storage, and remote caching remain separate follow-up optimizations.

[github-actions]

Supabase CLI preview

npx --yes https://pkg.pr.new/supabase/cli/supabase@2120ca84f4f749277ae46f5db4014d8cb00eb1e7

Preview package for commit 2120ca8.