[lore] Flesh out /timeline/ — Zombie Stage AU vs mainline ALNST

[zombiestageweb]

/timeline/ is currently a stub. Turn it into the definitive
Zombie Stage AU vs mainline Alien Stage timeline reference.

Structure

1. A short intro: Zombie Stage is an AU, not a sequel to KARMA.
2. A two-column table: mainline ALNST beats ↔ Zombie Stage beats.
3. In-universe chronology of Zombie Stage rounds as they release.
4. Cross-links to the individual _rounds/ pages.

Rules

• Anything not directly shown / stated by VIVINOS goes under ## Speculation.
• Cite the Fandom wiki for mainline ALNST beats.

Tracker: #1

[zombiestageweb]

Where this will land

The AU timeline publishes to zombiestage.com/guide/au-timeline/.

Scope

• In scope: how Zombie Stage's Round 1 lines up alongside mainline Alien Stage events, and how Rounds 2–6 (once known) will fit.
• Out of scope: exhaustive mainline ALNST timeline — link to Fandom for that.

Edit target: timeline/index.md. Sources should be VIVINOS' own uploads / posts.