Summary

Closes #547.

Previously, the calculated duration (e.g. "2 years 3 months") was only ever appended to the DATE placeholder's value, joined by two newlines, with no way for a custom entry template to access it on its own. This made it impossible to position the time span independently in a custom layout, which is exactly what was reported in #547.

process_date now returns (date_string, time_span_string) instead of a single pre-concatenated string. DATE keeps its exact existing value for full backward compatibility with themes that only ever used DATE; when show_time_span is true, TIME_SPAN is also added to entry_fields so custom templates can reference it directly.

Changes

• src/rendercv/renderer/templater/entry_templates_from_input.py: process_date returns a tuple; render_entry_templates sets DATE (unchanged output) and, when applicable, the new TIME_SPAN field.
• tests/renderer/templater/test_entry_templates_from_input.py: updated the two existing tests whose assertions depended on process_date's old return type, and added two new tests covering the actual fix (TIME_SPAN available on its own, and correctly dropped when show_time_span is false).
• docs/user_guide/yaml_input_structure/design.md: mentioned TIME_SPAN where the Templates section already lists available placeholders, since that's the doc the issue reporter would have read and found no mention of it.

Testing

• Reproduced the reported bug against the issue's own example config before making any change (confirmed TIME_SPAN silently vanished from output).
• Full suite passes: just test (1540 passed).
• just check (ruff + ty) clean.
• Confirmed byte-identical output on the default classic theme with show_time_spans_in enabled, to verify backward compatibility.

Note

This is my first PR to this project. I set up the dev environment via the developer guide and worked through this with Claude Code, per the suggestion in #672.