docs(miner-deployment): write laptop-mode vs fleet-mode deployment guide

[JSONbored]

Write a standalone deployment guide comparing the two Phase 6 form factors — slim laptop mode (SQLite, no Docker, npm install -g) and the Docker fleet image — so a contributor can pick the right one for their situation (single machine vs. running many parallel miner attempts). Pure documentation; no code changes.

Deliverables

• New packages/gittensory-miner/DEPLOYMENT.md (or a README section) with a comparison table: setup steps, dependencies, when to use which, resource footprint.
• A worked laptop-mode walkthrough: install, init, doctor, expected directory layout.
• A worked fleet-mode walkthrough: build/pull the image, mount /data, pass credentials via env, run.
• Explicitly document the invariant that both modes are 100% client-side (no required phone-home for core operation) and that credentials never leave the operator's machine.
• Link back to the main package README so the docs are discoverable from npm install -g @jsonbored/gittensory-miner.

References

• packages/gittensory-miner/ package README (from the packaging skeleton issue) — this guide extends it.
• Dockerfile (repo root) comment header — the tone/level of detail to match for the deployment invariants section.

[linear-code]

JSO-2427