docs: clarify local dev memory options

[royalpinto007]

Summary

• document the existing lower-memory local dev commands for machines where bun run dev:full stalls or consumes too much RAM
• fix the separate-server instructions to point to the actual app and realtime dev commands
• add a quick cache cleanup tip for stuck Next.js dev runs

Closes #5282

Testing

• git diff --check

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PR Summary

Low Risk
Documentation-only README edits with no runtime or application code changes.

Overview
Expands the Manual Setup local dev section so contributors on tight RAM or stuck bun run dev:full runs have clearer paths forward.

It documents existing root scripts dev:full:capped (4GB Next.js heap) and dev:full:minimal-registry (smaller block registry), replaces the old separate-server one-liner with explicit apps/sim and apps/realtime commands, and adds dev:clean when Next.js keeps a bad dev cache.

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[greptile-apps]

Greptile Summary

This PR updates the local development README guidance. The main changes are:

• Adds lower-memory alternatives for full local dev startup.
• Corrects the separate app and realtime server commands.
• Adds a quick Next.js dev cache cleanup tip.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed documentation.
• The documented commands match existing package scripts and expected working directories.

Important Files Changed

Filename	Overview
README.md	Clarifies local dev startup options and cache cleanup guidance without changing runtime code.

_{Reviews (1): Last reviewed commit: "docs: clarify local dev memory options" | Re-trigger Greptile}