fix: promote source under title, drop subtitle from problem files

[izolyte]

What & why

Removes the ambiguous by author | date | source meta line and places the problem
source prominently under the title. Also removes unused subtitle: fields from
existing problem files — the parameter remains available in the template.

Closes #5

Changes

Rendering

• Source link now appears directly under the title at 10.5pt italic — first thing
  the reader sees after the title
• Removed pipe-separated meta line that implied the author wrote the problem

Checklist

• Meets the authoring standard in docs/AUTHORING.md
• Every result used-but-not-proved carries a cite(...) — no red [ref?] markers left
• Source set in metadata: source + source_url, or source: "" for an original; correct source_license

Bilingual

• Thai file shares the English number, slug ends in -th, both compile

Notes

subtitle is intentionally kept in doc() signature — not removed, just unused
here. Future problems that need a subtitle can still pass one.

Summary by CodeRabbit

• Style
  • Updated document metadata display formatting. Source attribution now appears in a dedicated block directly under the document title, with linked sources displayed as clickable references.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d7be1d6e-d475-4019-8cff-cc2b70718702

📥 Commits

Reviewing files that changed from the base of the PR and between 46e2e78 and 8d1bea6.

📒 Files selected for processing (1)

• src/template.typ

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📝 Walkthrough

Walkthrough

In src/template.typ, the doc() function's header is modified: the pipe-separated meta line combining author, date, and source is removed and replaced with a conditional source attribution block that renders only when source is non-empty, optionally hyperlinking via source_url.

Changes

Source Attribution Block

Layer / File(s)	Summary
Conditional source attribution under title src/template.typ	Removes the combined author | date | source pipe-separated meta line (lines 115–126) and replaces it with a block that renders a source attribution only when source != "", using source_url as a hyperlink target when present; the short accent rule is repositioned to follow this new block.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• izolyte/math-showcase#3: Also modifies the doc(...) header rendering in src/template.typ, specifically the metadata presentation beneath the title.

Suggested labels

enhancement

🐇 A pipe-divided line once cluttered the page,
Author and date and source all in a cage.
Now source stands alone, linked clean and bright,
No ambiguous bylines to muddle the sight.
Hop hop — less noise, more signal tonight! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main changes: removing the pipe-separated metadata line and promoting source attribution under the title, while dropping subtitle fields from problem files.
Linked Issues check	✅ Passed	The PR successfully addresses all coding requirements from issue #5: removes pipe-separated meta line, adds source link under title in template, removes subtitle fields from problem files, and retains subtitle parameter for backward compatibility.
Out of Scope Changes check	✅ Passed	All changes are directly aligned with the stated scope of issue #5 and PR objectives: template rendering modifications, metadata restructuring, and subtitle field removal from problem files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/template-source-attribution

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