Fix packaged Next client boundaries

[0thernet]

Outcome

• Emit one valid top-level client directive in each published browser entry.
• Preserve the shared client singleton and every existing export boundary.
• Publish coherent package, inventory, and README version 0.1.2.

Reproduction

The exact packed v0.1.1 artifact fails a real Next 16.2.12 App Router build. dist/client.js retains a second client directive after bundled expressions, and dist/react.js retains one after imports. Next rejects both as misplaced directives.

Validation

• bun run check
• 29 deterministic tests and four property tests
• genuine Node 24 ESM and CommonJS imports of every packed export
• Bundler and NodeNext type resolution from the packed archive
• real App Router builds on exact Next 16.2.12 and 16.3.1 importing both client and react
• exact directive-shape assertions in generated dist and each installed archive
• bun pm pack --dry-run --ignore-scripts
• independent read-only exact-diff review with no actionable findings