… naming

- Extract shared EXCLUDED_DIRS, frontmatter_re(), doc_type_tag() into
  new vault_utils.rs module (was duplicated across 3 modules)
- Fix fix_broken_yaml_list() which silently skipped instead of replacing
  bare tags: with tags: []
- Remove module-level #![allow(dead_code)] from check_links.rs
- Change check-tags --scope from string to TagScope enum
- Rename graph orphans --min-importance to --min-chars for clarity

- Unify normalize-frontmatter from --dry-run to --fix for CLI consistency
- Add reverse index (BTreeMap) for O(1) wikilink target resolution
- Eliminate double txt_stems linear search in check_links
- Remove unused PRIMARY_FILES/SUPPLEMENTARY_DIRS constants
- Track per-issue fixed status instead of batch marking all issues
- Simplify orphans regex: [\s\S]*? → .*? with (?s) flag
- Add frontmatter_re() regex safety comment

…p tests

- Replace trim_end_matches(".md") with strip_suffix(".md") to prevent
  incorrect truncation (e.g. "README.md" → "READ")
- Add collision guard for .txt→.md rename when .md already exists
- Fix /seeded/ path matching to handle root-level and backslash paths
- Migrate check_links tests from manual temp dirs to tempfile::TempDir
- Fix collect_txt_stems doc comment (set → map)
- Add regression test for strip_suffix behavior

- Add stem collision warning in build_stem_index (check_links.rs)
- Extract check_missing_tag and apply_tag_fixes helpers (check_tags.rs)
- Decompose check_links into handle_extension_mismatch + handle_filename_mismatch
- Replace BrokenLink.issue String with LinkIssue enum for type safety
- Add fs::metadata pre-filter in detect_orphans before reading content

- Guard fs::rename in handle_filename_mismatch with target existence
  check to prevent silent data loss
- Unify scan_project_docs no-frontmatter handling with shared
  check_missing_tag + apply_no_frontmatter_fixes pattern
- Replace info! with warn! on failure paths in check_links
- Add test for rename content preservation
- Add test for project doc no-frontmatter fix

Co-Authored-By: Claude Opus 4.7 <[email protected]>