feat(emulate): add --slug option to namespace portless aliases

[gmackie]

Summary

Adds a --slug option to emulate start and emulate init that namespaces portless aliases per project.

Motivation

Each emulate instance holds mutable runtime state (issues, customers, messages, sessions, etc.) with no tenant isolation, so running multiple projects against a single instance causes state crosstalk. Running separate instances per project is a simple solution — tenant-level namespacing would also work but would be a significant overhaul to the project.

In port-based mode, separate instances are trivial — just use different --port ranges. But in --portless mode, aliases are derived solely from the service name (github.emulate, stripe.emulate). A second instance silently overwrites the first's aliases via --force, and shutdown of either instance removes the alias for both. --base-url can't help here — it's mutually exclusive with --portless and only affects advertised URLs, not alias registration.

--slug namespaces both the portless alias and the advertised URL, allowing concurrent instances without collisions.

Changes

• Add --slug to start and init commands
• Read slug from config file (slug top-level key), CLI flag takes precedence
• Validate slug as a DNS label (lowercase alnum + hyphens, max 63 chars)
• Register portless aliases after servers bind to avoid dangling aliases on port conflicts
• Update init output to suggest --portless when slug is configured
• Update README, docs site, and SKILL.md

Usage

# emulate.config.yaml
slug: myapp
tokens:
  # ...
github:
  # ...

# Or via CLI flag (overrides config)
npx emulate start --portless --slug myapp

# URLs: https://github.myapp.emulate.localhost
#        https://stripe.myapp.emulate.localhost

emulate init --slug myapp writes the slug field to the generated config. Without --slug, no slug is written and portless behaves as before.

Test plan

• --portless --slug myapp registers aliases as github.myapp.emulate and serves at https://github.myapp.emulate.localhost
• --portless without slug behaves identically to before
• --slug without --portless errors with a clear message
• Invalid slugs (spaces, uppercase, special chars) are rejected
• Two instances with different slugs run concurrently without alias collisions

🤖 Generated with Claude Code

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