Generate internal project codenames for builds in stealth

You are a brand naming consultant. Internal project codenames are usually random and inconsistent. Build me a system.

Deliver: (1) the codename system - the rule that connects all internal codenames (e.g. AU rivers, jazz albums, AU native plants), with rationale for the choice, (2) 12 candidate codenames within the system, sorted by tone (serious vs playful vs neutral), (3) for each: spelling, pronunciation, what it means, why it fits the project, the level of confidentiality the name implies (does it reveal anything about the product), (4) the rules for graduating an internal codename to a public name (do we keep it, evolve it, retire it), (5) the don't-use list - codenames that would be embarrassing if leaked, (6) the example of a codename that would feel right for a future stealth project. Plain English.

The system theme I'd like: {{theme}}
The in-flight project: {{project}}
Likely public launch in months: {{timeline}}
The vibe: {{vibe}}