chore: removed the next folder from the cli directory

[Prashansa-K]

Summary

next version of the CLI is a scraped project at the moment. Thus, removing these files so as to reduce confusion.
If required in future, we can always access these via git history.

Brief of changes

• Restored genuinely-shared infrastructure from next/ into src/shared/ (auth, config, cli/command-docs) with corrected import paths, since legacy actually depends on it.
• Fixed all downstream breakage: import paths across shared/cli/run.ts, telemetry layers, test helpers (mocks.ts), and scripts/generate-docs.ts.
• Modified release tooling to drop the next/alpha shell entirely.
• Removed unused dependencies.
• Rewrote a few things so that references of next could be removed from tests, test-helpers or docs.

Deliberately left untouched

apps/cli/AGENTS.md and apps/cli/CLAUDE.md — describes the stale two-shell architecture
apps/cli/docs/platform-command-generation.md — documents supabase api routes/api request, a feature that only ever existed in next/.
apps/cli/docs/go-cli-divergences.md
The above documents can be changed later once we shift the legacy CLI directly under src.

Checklist

• The PR title follows Conventional Commits (e.g. fix(cli): …).
• Tests added or updated for the change - NA.
• From the repository root, pnpm check:all passes; relevant package tests pass for every touched workspace, and pnpm types:check passes for each touched TypeScript workspace (or workspace declaring it).

[github-actions]

Supabase CLI preview

npx --yes https://pkg.pr.new/supabase/cli/supabase@3b9c0f0c6bbcd3be597875b64c23ac7c2ddd12cd

Preview package for commit 3b9c0f0.

[Coly010]

Reviewed the full diff against origin/develop (06af58c) in a local worktree: pnpm types:check, pnpm exec knip-bun, and the full unit (324 files / 5593 tests) + integration (141 files / 3382 tests) suites all pass clean. The next/ → shared/ moves and the release/CI workflow changes (dropping the alpha channel) are internally consistent — traced every non-mechanical rename and found no dangling references.

A few things outside this diff worth a follow-up, since they aren't on the PR description's own "deliberately left untouched" list:

• Root README.md:132 — the onboarding quickstart still runs pnpm dev:next -- --help, which now fails with ERR_PNPM_NO_SCRIPT since dev:next is removed from apps/cli/package.json (reproduced locally).
• apps/cli/CLAUDE.md / AGENTS.md — understood these are intentionally deferred per the PR description, but flagging that they currently describe a three-tree legacy/next/shared architecture and a next/-dual-write obligation that no longer applies, and claim next/ is "moving to a dedicated branch" — there's no such branch in the remote; it's just being deleted with git history as the fallback. Worth prioritizing given how directly these files steer both contributors and coding agents working in this package.
• apps/cli/docs/ui.md — still documents @effect/atom-react / ink / ink-spinner as "the recommended approach" for terminal UI, with examples lifted from the deleted StartDashboard.tsx. None of those packages remain in package.json after this PR.

Also worth calling out explicitly in the PR description rather than folding into the general chore: scripts/generate-docs.ts now builds the docs-site command reference from legacyRoot instead of nextRoot — looks like this silently fixes a latent bug where the public CLI reference docs were being generated from the experimental v3 tree instead of the actually-shipped legacy CLI.

[Prashansa-K]

Added a disclaimer line in cli/AGENTS.md about scraping of next/ for now.
Not revising it yet, as I we may have to revisit it again once we get rid of legacy and move everything directly under src.