Migrate default dev setup to dynamic port allocation

[vnv-varun]

Context

PR #2440 adds isolated parallel dev environments with dynamic port allocation as an opt-in (pnpm setup-dev --isolated <name>). The default pnpm setup-dev still uses docker-compose.dbs.yml with fixed ports.

This ticket covers making dynamic ports the default for all developers, retiring the fixed-port setup entirely.

Why

Simplifies the setup story — one path instead of two. Every developer gets the same isolation benefits (no port conflicts, parallel-ready) without needing the --isolated flag.

Surface areas to update

File	Change needed
packages/agents-core/src/setup/setup.ts:70-73	Replace hardcoded REQUIRED_PORTS (5432/5433/5434) with post-startup health check
packages/agents-core/src/auth/authz/config.ts:15	Remove localhost:50051 fallback — require env var
agents-api/src/workflow/world.ts:36	Remove localhost:5432 fallback — require env var
package.json (3 zed commands)	Read SPICEDB_ENDPOINT from env instead of hardcoded localhost:50051
.github/workflows/ci.yml	Dynamic port discovery in CI
.github/workflows/cypress.yml	Same
.env.example	Update examples for dynamic mode

Dependencies

• Requires feat: isolated parallel dev environments #2440 to be merged first

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