feat: add refine command to improve drafts against SeoBrief

[fmueller]

Motivation

• Provide a CLI workflow step to improve an existing draft against a validated SEO brief and optional feedback so the content is ready for meta and translate.
• Allow writers to refine only selected sections and control rewrite aggressiveness and evidence requirements via --section, --intensity, and --evidence options.
• Keep refinements grounded in the original note when provided to avoid inventing facts and preserve Markdown structure where possible.
• Offer optional prompt artifact saving and a concise changelog to aid review and auditing of edits.

Description

• Add a new command scribae refine (registered in src/scribae/main.py) implemented in src/scribae/refine_cli.py with flags matching the design (--in, --brief, --note, --feedback, --section, --intensity, --evidence, --out, --dry-run, --apply-feedback, --changelog, --preserve-anchors, --save-prompt).
• Implement core refinement logic in src/scribae/refine.py including draft parsing (parse_draft), section mapping to the SeoBrief outline, snippet selection via snippets.build_snippet_block, LLM invocation, evidence handling, intensity modes, prompt artifact saving, and optional changelog generation.
• Add prompt templates in src/scribae/prompts/refine.py with SYSTEM_PROMPT, per-section user prompt builder, and changelog prompt builder; update src/scribae/prompts/__init__.py accordingly.
• Add tests and fixtures: tests/fixtures/draft.md and tests/unit/refine_cli_test.py exercising full refine flow, section-range behavior, evidence handling, dry-run feedback inclusion, and changelog output.

Testing

• Ran uv run ruff check and fixed style issues; result: passed.
• Ran uv run pytest and observed all tests passing: 121 passed.
• Ran uv run mypy which reported type-check failures due to missing torch stubs in src/scribae/translate/mt.py and is therefore not green.
• Manual smoke behavior verified via unit tests that scribae refine --in draft.md --brief brief.json --out refined.md produces refined markdown and respects --section, --intensity, --evidence, --dry-run, and --changelog options.

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Codex Task