Add interactive tern-cli package and dashboard handler snippet support

[Prateek32177]

Motivation

• Provide an interactive CLI to guide users through webhook handler setup and local testing for the tern ecosystem.
• Surface provider/framework context to the UI so the dashboard can offer ready-to-copy handler snippets.

Description

• Introduces a new package @hookflo/tern-cli with an interactive wizard (src/wizard.ts), file generators (src/files.ts), tunnel orchestration (src/tunnel.ts), platform/framework templates (src/templates.ts) and small utilities (browser.ts, clipboard.ts, colors.ts, config.ts, index.ts) plus TypeScript types and tsconfig.json and README.md.
• Adds handler templates and path generation logic for multiple platforms and frameworks and writes tern.config.json automatically with ensureConfig when needed.
• Integrates CLI tunnel output with @hookflo/tern-dev and copies the public relay URL to the clipboard and prints a formatted box for easy provider configuration.
• Extends core tern-dev to include platform and framework in TernConfig, exposes them via the UI status endpoint, and updates tern-config.schema.json accordingly.
• Enhances the UI (src/ui/index.html) and client JS to detect provider headers, surface a snippet FAB/popup, generate framework-aware handler snippets, copy snippets to clipboard, and show snippet suggestions when events arrive.

Testing

• Performed TypeScript typecheck for the new CLI package using tsc --noEmit -p packages/tern-cli/tsconfig.json, which completed successfully.
• Ran the repository test suite (pnpm test) and existing tests passed after the changes.

---

Codex Task