refrakt format re-indents nested block tags, with a check mode and editor formatting

Acceptance Criteria

• refrakt format [paths] re-indents .md files by SPEC-170 D5: one tab per level of block-tag nesting, applied only inside a block tag that contains another block tag; inline tags do not count
• It changes only the leading whitespace of lines inside block tags; every other byte is unchanged, asserted on fixtures that include lists, tables, emphasis and long tag openings
• A fenced code block keeps its internal relative indentation and is shifted as a whole
• It writes a file only when the AST parsed with the shared parse is unchanged; otherwise it reports the file and line and leaves the file alone
• Formatting is idempotent: a second run changes nothing, asserted on every fixture
• refrakt format --check exits non-zero and names each file that would change; CI runs it beside npm run format:check (.github/workflows/format.yml)
• The language server provides document formatting with the same function, so editors can format on save
• Every file under plan/ is unchanged by a run, asserted once in the resolution
• The MCP server exposes it, or the resolution records why not
• The composed-runes guide and the content-authoring docs state the rule and the command