chore(comfort): Add semantic line-break Rust/Markdown formatter

[JeanMertz]

comfort is a new contrib crate that reformats Rust doc comments (///and//!) and Markdown files using semantic line breaks — one sentence per line — with an optional --max-width` safety net for long sentences.

The pipeline runs in three layers: extract finds doc-comment blocks
via ra-ap-rustc_lexer, reflow_markdown parses each block's body with
comrak and walks the AST to locate reflowable paragraphs, and
reflow_paragraph segments those paragraphs into sentences using a UAX
#29 splitter with abbreviation-aware merging.

Markdown structure (headings, code blocks, tables, block quotes, lists,
footnotes, hard line breaks) is preserved verbatim; only prose paragraph
contents are reflowed. Container blocks (block quotes, list items, task
items, alerts, footnote definitions) each contribute the correct
per-line continuation prefix so reflow output round-trips cleanly.

Two optional passes compose on top of the always-on sembr engine:

• --format-markdown: canonicalizes markdown structure via comrak's
  format_commonmark (normalizes list markers to -, prefers fenced
  code blocks, aligns table columns for visual display width including
  CJK wide characters) before reflowing.
• --reference-links: converts inline [text](url) links to
  reference-style [text] with definitions consolidated and sorted
  alphabetically at the bottom of each body.

Both transformations are idempotent individually and when composed.

The tool ships two binaries from the same entry point: comfort (direct
invocation, defaults to stdin/stdout) and cargo-comfort (cargo
subcommand, defaults to --workspace). Common flags: --check,
--list-changed, --workspace, -p/--package, --exclude,
--language, --stdin-filename, --max-width.

A new fmt-comments-ci justfile target runs comfort --check --workspacein CI, added to theci recipe alongside the existing
fmt-ci step.