fix(lychee): exclude self-referential URLs and fix stale GitHub branch-protection docs link

[ichoosetoaccept]

Closes DOT-493
Closes DOT-494

Summary

• Add three exclusion patterns to project/.lychee.toml.jinja for URLs that 404 on a fresh scaffold:
  • {repository_host}/{repository_namespace}/{repository_name}/... — covers workflow badges, action queries, the discussions URL, etc.
  • {repository_namespace}.github.io/{repository_name}/... — covers the GitHub Pages docs site that doesn't exist before first deploy.
  • pypi.org/project/{distribution_name} — only emitted when publish_to_pypi; won't exist before first release.
• Replace the stale GitHub branch-protection docs link in project/README.md.jinja with the current about-protected-branches page.

Why

These URLs all 404 the first time lychee runs on a freshly scaffolded project (before the GitHub repo exists, before CI has run, before docs deploy, before publishing). They're user-owned anyway — lychee can't tell us anything we don't already know — so excluding them removes the noise without losing any real protection.

DOT-493 originally proposed enabling Discussions via the post-scaffold gh repo edit task. This PR takes the opposite approach: it stops lychee from gating the first commit on a feature the user may not want enabled. Either solution closes the user-visible bug.

Test plan

• poe test — green
• Run lychee against a freshly rendered project — 0 errors, 7 excluded
• Full first-commit e2e regression coverage added in test(scaffold): add full first-commit e2e regression test #310

[ichoosetoaccept]

This change is part of the following stack:

• fix: scaffolded files end with single trailing newline #306
  • fix(prek): keep lychee on a versioned tag after autoupdate (DOT-492) #307
    • fix(scaffold): ship placeholder pytest file so first commit succeeds (DOT-491) #308
      • fix(lychee): exclude self-referential URLs and fix stale GitHub branch-protection docs link #309 ◀
        • test(scaffold): add full first-commit e2e regression test #310

_{Change managed by git-spice.}

[linear]

DOT-493 Post-scaffold task should enable GitHub Discussions

DOT-494 Stale `docs.github.com` branch protection URL in README.md returns 404

[greptile-apps]

Greptile Summary

This PR adds three lychee regex exclusion patterns in .lychee.toml.jinja to suppress false-positive 404s on URLs that can't exist until after a repo is created, CI runs, docs deploy, and a package is published. It also replaces a stale GitHub branch-protection docs link in README.md.jinja with the current about-protected-branches page.

Confidence Score: 5/5

Safe to merge — all changes are targeted exclusion patterns and a doc link fix with no logic regressions.

No P0 or P1 findings. The exclusion regexes are correctly anchored with (/|$), the Pages-URL pattern is properly guarded by repository_host in ['github.com', 'gitlab.com'], and the PyPI pattern is guarded by publish_to_pypi. The README link replacement is a straightforward dead-link fix. Previously noted dot-escaping concern was already addressed in prior review threads.

No files require special attention.

Important Files Changed

Filename	Overview
project/.lychee.toml.jinja	Adds three conditional exclusion patterns for self-referential repo URLs, GitHub/GitLab Pages URLs, and PyPI project URLs; all patterns are correctly anchored and guarded by appropriate Jinja conditions.
project/README.md.jinja	Replaces the stale GitHub branch-protection docs URL with the current about-protected-branches permalink; no logic changes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[lychee runs on scaffolded project] --> B{URL matches exclusion pattern?}
    B -->|Self-referential repo URL\nhost/namespace/repo/*| C[Skip — repo doesn't exist yet]
    B -->|GitHub/GitLab Pages URL\nnamespace.host.io/repo/*| D[Skip — docs not deployed yet]
    B -->|PyPI project URL\npypi.org/project/distname| E[Skip — package not published yet\nonly if publish_to_pypi]
    B -->|No match| F[Check URL]
    F --> G{HTTP status}
    G -->|Accepted: 200,204,301,302,403,429,502| H[Pass]
    G -->|Other| I[Fail / report]

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