feat(template): add new systemprompt template

[Ejb503]

feat(template): add new systemprompt template

Adds systemprompt, a self-owned AI control plane: a governance gateway for Claude, OpenAI, and Gemini with policy checks, request audit, rate limits, cost tracking, and MCP server orchestration. Bundles Postgres.

Changes

• templates.json: new type-3 template, id 76
• stacks/systemprompt/docker-compose.yml: the stack file (app + Postgres, named volumes, healthchecks)

Details

• Image is publicly pullable: ghcr.io/systempromptio/systemprompt-template:0 (floating major tag; minor/patch releases need no template bump).
• Requires at least one AI provider API key, surfaced as env vars with defaults and a note.
• First boot runs DB migrations and a publish pipeline; the app healthcheck has a 300s start period to cover it.
• Tested end to end: deployed through a local Portainer CE 2.39.5 instance using this exact template JSON and compose file, stack reached healthy, /api/v1/health returns {"status":"healthy"}.
• templates.json validates against schema.json (same check as the validate workflow).