feat: add managed proxy-host Nginx configuration deployments

[Lorwell]

Why

This adds a managed, per-proxy-host Nginx configuration workflow so users can define structured listener, proxy, header, and location settings; preview the rendered configuration; and deploy it safely. It also exposes a live Nginx log viewer to make host-level troubleshooting possible from the UI, and includes SQLite-oriented local development tooling.

The deployment path renders and validates candidate configuration before an atomic swap/reload, records desired versus applied state, and recovers or rolls back interrupted/failed deployments.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• API changes
• Performance improvement
• Test addition or update

AI Usage

• AI was used to write this
• AI was used to review this

Implementation summary

• Adds proxy-host Nginx configuration persistence, normalization, deterministic rendering, validation, preview tokens, diagnostics, and desired/applied deployment records.
• Adds atomic deployment, reload rollback, and interrupted-deployment recovery, plus migration and focused backend test coverage.
• Extends the API and Proxy Host UI with structured configuration fields, previews, deployment state, and a live Nginx log viewer.
• Adds SQLite development compose/start tooling and a Docker Hub image publishing workflow.

Validation

• pnpm --dir backend test: 27 passed; 1 skipped because the local better-sqlite3 native binding is unavailable.
• pnpm --dir frontend exec tsc --noEmit
• git diff --check origin/develop..HEAD