Point the repo-root install at the Go node

[AbirAbbas]

Why

The Go node in go/ is the maintained SWE node — same reasoners, same
interface, one static binary, and it ships the coding engine. Until now
getting it meant knowing to append //go, and anyone who installed this repo
earlier stayed on the Python node with no way across.

What

The root manifest declares itself superseded by the Go node:

name: swe-planner
superseded_by: https://github.com/Agent-Field/SWE-AF//go

So this becomes the one thing a user has to know, before and after the switch:

af install https://github.com/Agent-Field/SWE-AF

It installs the Go node, and replaces an existing swe-planner — warning
first, and carrying that node's secrets across.

The Python node is unchanged and still what python -m swe_af and the Docker
images run; this manifest stays as the redirect. To install it deliberately,
clone the repo and install the checkout as a local path.

Requires

superseded_by support in agentfield (Agent-Field/agentfield#872). An older
af ignores the key and installs the Python node exactly as before, so this
is safe to land in either order.

Verified end to end

Against a real repo containing this manifest and the go/ node with its
bundled engine binary:

• af install <repo url> warns, then installs swe-planner-go — the Go node,
  engine binary present at 0755 with a matching checksum
• the recorded source keeps the //go selector, so the next update stays on
  the Go node instead of reverting to Python
• with an existing swe-planner installed: warned, replaced, its node-scoped
  secret moved to the successor, old registry entry and directory removed,
  global secrets untouched
• started with only an OPENROUTER_API_KEY: the node registered its 31
  reasoners, the harness ran opencode … -m openrouter/deepseek/deepseek-v4-flash,
  and the bundled engine stayed off (it is opt-in via SWE_PRO_ENGINE)
• triggered implement_issue and it succeeded, delivering a branch with the
  requested function plus a passing pytest test

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🤖 Generated with Claude Code

[AbirAbbas]

Folded into #122 — the root-manifest redirect belongs with the release that makes the Go node the thing you get, so it is one PR rather than a stacked pair. Commit b0a7514 carries it there unchanged.

Superseded by #122