docs: sharpen README positioning

[charlieijk]

Adds a concise product-level tagline above the existing detailed README. No runtime behavior changes.

Summary by CodeRabbit

• Documentation
  • Updated the README to describe Strata as a deterministic expedition game powered by an authoritative world simulation.

[coderabbitai]

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Free

Run ID: c70112ad-3274-4701-be1d-0d1e34cb175a

📥 Commits

Reviewing files that changed from the base of the PR and between 2f53822 and d6ab93f.

📒 Files selected for processing (1)

• README.md

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📝 Walkthrough

Walkthrough

README.md now describes Strata as a deterministic expedition game backed by an authoritative Go world simulation.

Changes

Documentation update

Layer / File(s)	Summary
README description README.md	Adds a concise description of Strata and its Go world simulation.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to d6ab9

This change only adds concise README positioning text and does not alter runtime behavior; no actionable merge-blocking risk remains.

Poem

A rabbit reads the README bright,
“Strata maps the world just right.”
Deterministic paths unfold,
Go keeps every tale controlled.
Hop, hop, clear words take flight!

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