Restored GitHub PR delegation and Forgejo PR link output

Summary

Fixed a regression where Codex.app could see Forgejo PR data but GitHub repositories reported PR info unavailable. The local config contained github.com in the Forgejo allowlist; the shim now ignores that host and delegates GitHub repositories to the real gh. I also added simple --template rendering so Forgejo PR URL probes can return a bare URL for click-through behavior.

Changes Made

Context

The observed machine config had hosts = ["git.deltaisland.io", "git.dirtydishes.dev", "github.com"]. Before this change, that made GitHub PR commands route through the Forgejo compatibility layer and return empty PR data. IslandFlow still produced URL fields in JSON, but newer Codex.app link probes may ask the GitHub CLI to format a single URL with --template; the shim parsed that flag but previously ignored it.

Important Implementation Details

• Config.is_forgejo_host("github.com") now returns false even if github.com is present in the stored config or FJ_SHIM_HOSTS.
• add_host("github.com") writes an empty host list instead of preserving an unsafe GitHub allowlist entry.
• Template rendering is intentionally small and compatibility-focused: it supports field replacements like {{.url}}, {{.currentBranch.url}}, and {{.}}, not full Go template logic.
• The existing stale config file does not have to be edited immediately for the code fix to work, because loaded config filters GitHub hosts in memory.

Relevant Diff Snippets

Focused excerpt rendered with Diffs server-side rendering via @pierre/diffs/ssr and embedded as static iframe content. It covers the host guard and template output path; regression tests and docs are summarized in prose to keep this file reviewable.

Expected Impact for End-Users

Codex.app should stop treating GitHub repositories as Forgejo, so GitHub PR info can come from the real GitHub CLI again. Forgejo repositories such as IslandFlow should keep returning PR data and can now answer URL-only template probes with a direct link like https://git.dirtydishes.dev/dirtydishes/islandflow/pulls/23.

Validation

• Ran python3 -m unittest -q: 93 tests passed.
• Ran PYTHONPATH=src python3 -m compileall -q src tests: passed.
• Verified source routing now delegates github.com/dirtydishes/gh-forgejo-shim and routes git.dirtydishes.dev/dirtydishes/islandflow.
• Verified the shimmed IslandFlow command gh pr status --json number,title,url --template '{{.currentBranch.url}}' returns the bare PR URL.
• Verified the GitHub smoke command delegates through native gh repo view github.com/dirtydishes/gh-forgejo-shim --json nameWithOwner,url.

Issues, Limitations, and Mitigations

• The simple template renderer does not implement full Go templates. It is scoped to the direct field substitutions Codex-style URL probes need.
• The installed pipx shim is still version 0.1.0 until the local package is reinstalled or released. The source fix was validated with PYTHONPATH=src.
• The stale github.com entry may remain in the text config file, but the runtime now ignores it. A future config write will omit it.

Follow-up Work

• Reinstall or release the package so Codex.app uses this fixed shim outside source-tree validation.
• Consider expanding template support if future Codex.app probes use range, conditionals, or formatting helpers.
• Optionally add a doctor warning that explicitly names ignored GitHub hosts found in the raw config file.