Triage and resolve stale TODO comments

[StephanMeijer]

Problem

9 TODO comments scattered across the codebase, some clearly outdated. The most visible one is the @moduledoc on Validation.Writer which literally reads "TODO: proper description" — this shows up on HexDocs.

Inventory

File	Line	TODO
lib/docspec/core/validation/writer.ex	2	@moduledoc "TODO: proper description"
lib/docspec/spec/schema.ex	211	"Be more descriptive of what the error is"
lib/docspec/core/html/writer.ex	475	"Research if we should use CSS" for <ol type>
lib/docspec/core/docx/reader/convert.ex	171	"detect and convert image captions"
lib/docspec/core/docx/reader/convert.ex	210	"handle w:r with w:instrText hyperlink field code"
lib/docspec/core/docx/reader/files/styles.ex	20	"get the style type from the based_on value"
lib/docspec/core/docx/reader/files/styles.ex	89	"implement looking up paragraph type using basedOn"
lib/docspec/core/docx/reader/files/styles.ex	94	"implement converting character, numbering and table style types"
lib/docspec/core/docx/reader/convert/paragraph.ex	26	"move Content to a shared location"

Proposal

For each TODO:

1. Resolve if the fix is straightforward
2. Convert to a GitHub issue if it's a real feature/improvement worth tracking
3. Remove with a comment if it's a deliberate "won't fix"

Priority: fix the @moduledoc "TODO: proper description" first since it's publicly visible in generated documentation.