chore: restructure as multi-language SDK monorepo

[akshitsinha]

Reorganizes the repo to support multiple language SDKs while keeping one synchronized release.

Layout

• Moved TypeScript SDK from packages/flagship to packages/typescript.

Release flow (Changesets)

• One release PR for all SDKs: chore(release): version SDK packages.
• .github/changeset-version.ts now:
  1. Validates pending changesets (unknown packages and non-SDK-only changesets fail fast).
  2. Expands any SDK changeset to bump every SDK with the highest declared bump.
  3. Runs pnpm changeset version.
  4. Strict-syncs pyproject.toml/Cargo.toml versions; fails if a native manifest is missing a version = "..." line.
• privatePackages: { version: true, tag: true } so non-npm SDKs get versioned and tagged; language-specific publish workflows can subscribe to those tags.

CI

• New Changesets PR job runs pnpm run changeset:validate.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@cloudflare/flagship@13

commit: 0963354