docs: document Fastly/Deno/AWS/GCP host feasibility in README

[davidwkeith]

Summary

• Follow-up to the portability investigation (Investigate adding support for other cloud function providers #369, spec/portability.md, docs: investigate multi-provider portability feasibility #378/Multi-provider portability: implementation plan (tracking) #384): document the final state in the root README's "Running it" section rather than leaving the provider picture scattered across spec docs only.
• Retitled the self-hosted section to explicitly name VPS/homelab/NAS, and called out that no cloud account is required at all (home server, NAS, Raspberry Pi).
• Added an "On AWS, GCP, or any other cloud" callout naming ECS/Fargate, GCE/Cloud-Run-pinned-to-one-instance, and top indie hosts (Fly.io, DigitalOcean, Hetzner, Linode) — all the same @dwk/server Docker image, no code changes — linking to packages/server/README.md's existing detailed per-provider notes.
• Added a new "Deno Deploy (exploratory — not yet a supported host)" subsection summarizing @dwk/deno-host's current state: SQL shim + actor/alarm emulation implemented, queue + object-storage shims still gated, external libSQL/Turso dependency trade-off unresolved.
• Named Fastly Compute, AWS Lambda@Edge, and Puter as explicit non-goals (eventually-consistent/no store, not fetch-shaped, undocumented consistency respectively), linking to spec/portability.md for the full reasoning and re-evaluation triggers.
• Added spec/portability.md to the Documentation list.

No runtime code changed — this is a README-only documentation update summarizing conclusions that were already recorded in spec/portability.md, spec/packages/deno-host.md, and packages/server/README.md.

Packages affected

None (root README.md only — no publishable package touched).

Checklist

• Read the relevant spec(s) under spec/packages/ and updated them if behaviour changed — not applicable, no behaviour changed; this summarizes existing spec conclusions in the README
• Added/updated colocated tests (src/*.test.ts) — not applicable, no code changed
• Ran the local CI gate: pnpm lint && pnpm format:check && pnpm typecheck && pnpm build && pnpm test — ran npx prettier --check README.md (passes); full gate not run since no package code changed
• Added a changeset (pnpm changeset) if this touches a publishable package — not applicable, no publishable package touched
• Updated catalog.json / conformance/status.json if this adds a new mountable worker or changes conformance status — not applicable, no new worker or conformance change

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[davidwkeith]

The github-advanced-security check failure is not related to this diff — the job log shows it's GitHub's own Copilot autonomous code-review agent (autofind.js) failing before it even analyzes the change, with a platform-side error: CAPIError: 400 {"error":{"message":"The requested model is not supported.","code":"model_not_supported"}}. That's the agent's configured backend model (claude-opus-4.6) being rejected by GitHub's own completions API — nothing this PR (a README-only text change) can fix by pushing a commit. CodeQL and the Analyze jobs on the same run passed; the repo's actual CI gate (lint → format:check → typecheck → build → test) is separate and green/in-progress. Not taking any action here since there's nothing on the repo side to change; will keep watching in case GitHub re-runs it successfully.

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Generated by Claude Code

[davidwkeith]

Reviewed against CONTRIBUTING.md. Verified locally on this branch: pnpm lint, pnpm format:check, and npx prettier --check README.md all pass; docs-only change so the rest of the CI gate (typecheck/build/test) is unaffected — no publishable package touched, confirmed no .changeset/ entry is needed per §"Record a changeset."

Checklist conformance: section headings (Summary, Packages affected, Checklist) kept verbatim, unchecked items each carry a one-line reason rather than being deleted — matches the "leave unchecked with a reason" rule. Commit/PR title (docs: document Fastly/Deno/AWS/GCP host feasibility in README) follows Conventional Commits with no scope, correct for a repo-wide docs change.

Content checks: the new packages/server/README.md#deploying-to-aws-gcp-or-any-other-cloud anchor and the spec/portability.md / spec/packages/deno-host.md / spec/deno-deploy-design.md links all resolve to real sections/files on this branch.

One thing worth a look before merge — left as an inline comment on the Deno Deploy gaps paragraph: it'll go stale if PR #418 (KV-backed queue emulation) merges first, since that PR closes the queue gap this paragraph describes as still open. Not a reason to hold this PR, just flag it for whichever of the two merges second.

Also noting for visibility, not this PR's problem: the github-advanced-security check is failing on both this PR and #418 with model_not_supported from the Copilot code-review agent's backend — an infra/config issue upstream of the diff, not something fixable from here.

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