fix: scaffolded files end with single trailing newline

[ichoosetoaccept]

Summary

• Strip a redundant blank line from project/README.md.jinja, project/.github/actionlint.yaml.jinja and project/{{_copier_conf.answers_file}}.jinja so the rendered files end with a single trailing newline (matches end-of-file-fixer).
• Exclude the empty actionlint.yaml from the scaffold when use_blacksmith_runners is false.

Why

Without these fixes, the end-of-file-fixer prek hook auto-rewrites scaffolded files on the very first commit, which forces an extra git add && git commit cycle for every new project. Surfaces as part of the broader DOT-491 fresh-scaffold investigation but warrants its own PR.

Test plan

• poe test — green
• Generate fresh project, confirm no files are touched by end-of-file-fixer on first commit

[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.}

[greptile-apps]

Greptile Summary

This PR fixes trailing-newline issues across three template files (README.md.jinja, actionlint.yaml.jinja, {{_copier_conf.answers_file}}.jinja) using targeted Jinja2 whitespace-stripping operators ({%- -%} and -}}), and adds a _exclude rule to copier.yml so .github/actionlint.yaml is never generated as an empty file when use_blacksmith_runners is false. Each change is minimal and correct for its context.

Confidence Score: 5/5

Safe to merge — all changes are precise Jinja2 whitespace-control fixes with no logic regressions.

All four changes are narrow, well-targeted whitespace fixes (strip operators and an _exclude rule) that align with Copier/Jinja2 conventions and the keep_trailing_newline: true envop. No P0 or P1 findings were identified.

No files require special attention.

Important Files Changed

Filename	Overview
copier.yml	Adds _exclude rule to suppress actionlint.yaml generation when use_blacksmith_runners is false; consistent with the existing exclusion patterns.
project/.github/actionlint.yaml.jinja	Adds -%} to the opening if tag to strip the post-tag newline, eliminating the leading blank line in the generated YAML when use_blacksmith_runners is true.
project/README.md.jinja	Changes {% endif %} to {%- endif %} to strip the trailing newline before the tag, ensuring the generated README ends with exactly one newline.
project/{{_copier_conf.answers_file}}.jinja	Adds -}} to the to_nice_yaml expression to strip the trailing template newline, keeping only the newline embedded in to_nice_yaml output for a single EOF newline.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[copier copy / update] --> B{use_blacksmith_runners?}
    B -- false --> C[_exclude: skip actionlint.yaml generation]
    B -- true --> D[Render actionlint.yaml.jinja]
    D --> E["'{%- if use_blacksmith_runners -%}' strips leading + trailing newline"]
    E --> F[self-hosted-runner labels content]
    F --> G["'{%- endif %}' strips pre-tag newline"]
    G --> H[keep_trailing_newline preserves final newline]
    H --> I[actionlint.yaml: clean single trailing newline]
    A --> J[Render README.md.jinja]
    J --> K{use_ci and github.com?}
    K -- true --> L[Branch protection section rendered]
    L --> M["'{%- endif %}' strips pre-tag newline → single EOF newline"]
    K -- false --> N["'{%- endif %}' strips any whitespace → single EOF newline"]
    A --> O["Render answers_file.jinja"]
    O --> P["{{ _copier_answers | to_nice_yaml -}}"]
    P --> Q["'-}}' strips template trailing newline; to_nice_yaml provides its own newline"]
    Q --> R[answers file: clean single trailing newline]

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