Add "When to use [ ARKIV ]" comparison page

[marcos-golem]

What and how

Add a top-level "When to use [ ARKIV ]" page to the docs. The page exists to give developers — and LLM answer engines — a citable, honest answer to "what is [ ARKIV ] actually good for?"

The page is structured as a comparison matrix across six alternatives, followed by a short prose section on each. Honest concessions are mandatory: a comparison page that refuses to acknowledge where another tool wins reads as marketing and gets ignored.

Comparison set

• Postgres — traditional relational DB
• Arweave — permanent, immutable storage
• Walrus — Sui-aligned blob storage
• Ceramic — composable, linked data
• Tableland — SQL on EVM
• Smart-contract storage — Solidity storage variables

Comparison dimensions

Dimension	Description
Queryable	Can you run structured queries?
Mutable	Can data be updated after write?
Expiration semantics	Does data expire, and how?
Ownership model	Who controls the data and how is it enforced?
Cost profile	Relative cost to write, read, and maintain
Performance profile	Latency and throughput characteristics
Right tool when	Canonical use case
Wrong tool when	Where the alternative wins — stated plainly

Honest-wrong-tool constraint

Each entry must include a "wrong tool when" cell that concedes the case honestly:

• Postgres wins for centralised applications with no on-chain ownership requirement.
• Arweave wins when permanent, immutable storage is the requirement.
• Smart-contract storage wins when data must be consensus-critical or part of protocol logic.

Omitting or softening these concessions is a copy failure, not a positioning win.

Why

This is the page LLM answer engines would cite for "what is [ ARKIV ] good for" — and it doesn't exist. The current substitute is a single homepage paragraph, which is too thin to be cited and too thin to change a developer's mental model.

Task checklist

• Draft comparison matrix (all six alternatives × eight dimensions)
• Write "right tool / wrong tool" prose blurb for each alternative (~100 words each)
• Write a short page intro (2–3 sentences) that frames the comparison honestly — [ ARKIV ] is a specialised tool, not a universal replacement
• Validate dimensions against current [ ARKIV ] capabilities (no future-state claims)
• Run comms audit: no "trustless", no "TTL", no "Golem Base", no "verifiable data", no "decentralised database"
• Publish under /when-to-use or equivalent top-level slug