feat: add Fly.io deployment target

[PAMulligan]

Closes #30

Summary

Adds Fly.io as the fifth deployment target, following the exact pattern of the Railway target (#117): Fly.io builds the same hardened multi-stage Docker image as the Node.js target, so the runtime code is fully shared and templates/fly/ adds only the platform config on top.

Acceptance criteria

• --fly flag in setup-project.sh — copies the node-server Dockerfile/docker-compose.yml (the issue's "can reuse the Node.js Dockerfile", same single-source-of-truth approach the merged Railway PR used) plus templates/fly/fly.toml, writes a Fly-specific .env.example, and warns if flyctl is missing
• templates/fly/fly.toml with everything the issue asks for:
  • app name placeholder (fly launch --no-deploy adopts the file and writes the unique name back)
  • HTTP service on internal_port = 3000 with force_https
  • /health check ([[http_service.checks]]) gating every deploy
  • auto-scaling min 1 / max 3: min_machines_running = 1 + autostop/autostart; Fly has no max key in fly.toml — the ceiling is the Machine count, documented as fly scale count 3
  • PostgreSQL attachment reference: fly mpg create / fly mpg attach (sets the DATABASE_URL secret automatically; Managed Postgres is Fly's supported offering — unmanaged Fly Postgres is now explicitly unsupported upstream)
• deployment-config-generator skill — new Step 2e with the fly.toml template, secrets/Postgres commands, scaling notes, and a commented flyctl deploy --remote-only CI snippet; schema-intake target union and interview options updated too
• Generated project README — one-time setup, deploys, scaling, and migrations (via fly mpg proxy, since the production image prunes drizzle-kit — same caveat as Railway's preDeployCommand)
• pipeline.config.json — fly added to deployment.targets plus a fly settings block
• CI — templates/fly added to the required-directories check; no new snippets to type-check

Verification

• All fly.toml keys checked against the live fly.toml reference; every linked Fly.io docs URL curl-tested (all 200)
• bash -n and ShellCheck (--severity=warning, matching CI) pass on setup-project.sh
• pipeline.config.json and fly.toml parse cleanly
• End-to-end: ./scripts/setup-project.sh fly-e2e --fly generates a working project — Dockerfile, fly.toml, .env.example, and README section all present; test suite passes 20/20

Note: pre-existing typecheck regression (all targets, not this PR)

While e2e-testing, pnpm typecheck in the generated project fails with Cannot find name 'process'. This is not Fly-specific: pnpm add -D typescript now installs TypeScript 6, which no longer auto-includes node_modules/@types, and the copied templates/shared/tsconfig.json has no "types" field (CI's snippet check passes because templates/snippets/tsconfig.node.json sets "types": ["node"] explicitly). Every target generated today (--node, --railway, --lambda, --fly) hits this. The fix needs per-target tsconfig handling (Cloudflare wants workers types, not node), so it's left for a separate issue.

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