fix: 修复 tag/changelog 生成范围，增加 --auto 模式

- fix(get_tags): 使用 find_object+peel_to_commit 支持 annotated tag
- fix(changelog): insert_changelog_entry 替换覆盖逻辑，保留已有章节
- feat: parse_changelog_versions 按 semver 降序提取版本
- feat: sort_tags_by_semver 取代纯时间排序
- feat(tag --auto): 优先读 Cargo.toml/pyproject.toml，回退 commit 分析
- feat(changelog): 无 --from 时自动检测 changelog 最高已有版本
- refactor: TagInfo::version_name(), GitRepo::find_tag_by_version()

src/git/changelog.rs

@@ -409,8 +409,8 @@ pub fn generate_from_history(
     if let Some(from) = from_tag {
         repo.get_commits_between(from, to_ref)
     } else {
-        // Get last 50 commits if no tag specified
-        repo.get_commits(50)
+        // Get all commits from the beginning (no from_tag = initial changelog)
+        repo.get_commits(usize::MAX)
     }
 }
 
@@ -476,3 +476,137 @@ impl ChangelogEntry {
         self
     }
 }
+
+/// Extract version strings from Keep a Changelog content.
+/// Returns versions sorted by semver descending (highest first).
+/// Excludes "Unreleased".
+pub fn parse_changelog_versions(content: &str) -> Vec<String> {
+    use semver::Version;
+
+    let mut versions: Vec<String> = vec![];
+    for line in content.lines() {
+        let trimmed = line.trim();
+        if trimmed.starts_with("## [") {
+            if let Some(end) = trimmed.find(']') {
+                let version = &trimmed[4..end];
+                if version != "Unreleased" && !version.is_empty() {
+                    versions.push(version.to_string());
+                }
+            }
+        }
+    }
+    // Sort by semver descending so highest version is first
+    versions.sort_by(|a, b| {
+        match (Version::parse(a), Version::parse(b)) {
+            (Ok(va), Ok(vb)) => vb.cmp(&va),
+            (Ok(_), Err(_)) => std::cmp::Ordering::Less,
+            (Err(_), Ok(_)) => std::cmp::Ordering::Greater,
+            (Err(_), Err(_)) => std::cmp::Ordering::Equal,
+        }
+    });
+    versions
+}
+
+/// Insert a new changelog entry into existing changelog content.
+/// The new entry is placed after the header and before the first existing version section.
+/// If no existing version sections are found, the new entry is appended after the header.
+pub fn insert_changelog_entry(existing: &str, new_entry: &str) -> String {
+    // Find the first version section (## [x.y.z])
+    if let Some(first_ver_pos) = existing.find("\n## [") {
+        let (header, rest) = existing.split_at(first_ver_pos);
+        // Ensure new_entry ends with a blank line before the next section
+        let entry = new_entry.trim_end();
+        format!("{}\n{}\n{}", header.trim_end(), entry, rest)
+    } else {
+        // No existing version sections — append after header
+        format!("{}\n{}", existing.trim_end(), new_entry.trim_end())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_changelog_versions_extracts_versions() {
+        let content = "# Changelog\n\n## [0.2.0] - 2024-03-01\n### Added\n- feature B\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let versions = parse_changelog_versions(content);
+        assert_eq!(versions, vec!["0.2.0", "0.1.0"]);
+    }
+
+    #[test]
+    fn test_parse_changelog_versions_sorts_highest_first() {
+        // Versions in reversed order — should still return highest first
+        let content = "# Changelog\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n\n## [0.3.0] - 2024-04-01\n### Added\n- feature C\n\n## [0.2.0] - 2024-03-01\n### Added\n- feature B\n";
+        let versions = parse_changelog_versions(content);
+        assert_eq!(versions, vec!["0.3.0", "0.2.0", "0.1.0"]);
+    }
+
+    #[test]
+    fn test_parse_changelog_versions_excludes_unreleased() {
+        let content = "# Changelog\n\n## [Unreleased]\n### Added\n- wip\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let versions = parse_changelog_versions(content);
+        assert_eq!(versions, vec!["0.1.0"]);
+    }
+
+    #[test]
+    fn test_parse_changelog_versions_empty_content() {
+        let versions = parse_changelog_versions("");
+        assert!(versions.is_empty());
+    }
+
+    #[test]
+    fn test_parse_changelog_versions_no_versions() {
+        let content = "# Changelog\n\nSome description text.\n";
+        let versions = parse_changelog_versions(content);
+        assert!(versions.is_empty());
+    }
+
+    #[test]
+    fn test_insert_changelog_entry_between_header_and_existing() {
+        let existing = "# Changelog\n\nAll notable changes...\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let new_entry = "## [0.2.0] - 2024-03-01\n### Added\n- feature B\n";
+        let result = insert_changelog_entry(existing, new_entry);
+
+        // New entry should appear after header, before 0.1.0
+        assert!(result.contains("## [0.2.0]"));
+        assert!(result.contains("## [0.1.0]"));
+        let pos_new = result.find("## [0.2.0]").unwrap();
+        let pos_old = result.find("## [0.1.0]").unwrap();
+        assert!(pos_new < pos_old, "new version should be before old version");
+    }
+
+    #[test]
+    fn test_insert_changelog_entry_preserves_all_existing_content() {
+        let existing = "# Changelog\n\nAll notable changes...\n\n## [0.2.0] - 2024-03-01\n### Added\n- feature B\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let new_entry = "## [0.3.0] - 2024-04-01\n### Added\n- feature C\n";
+        let result = insert_changelog_entry(existing, new_entry);
+
+        assert!(result.contains("## [0.3.0]"));
+        assert!(result.contains("## [0.2.0]"));
+        assert!(result.contains("## [0.1.0]"));
+        assert!(result.contains("feature A"), "oldest content preserved");
+        assert!(result.contains("feature B"), "middle content preserved");
+        assert!(result.contains("feature C"), "new content present");
+    }
+
+    #[test]
+    fn test_insert_changelog_entry_empty_existing() {
+        let existing = "# Changelog\n\nAll notable changes...\n\n";
+        let new_entry = "## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let result = insert_changelog_entry(existing, new_entry);
+        assert!(result.contains("## [0.1.0]"));
+        assert!(result.contains("# Changelog"));
+    }
+
+    #[test]
+    fn test_insert_changelog_entry_extra_blank_lines_in_header() {
+        let existing = "# Changelog\n\n\n\n## [0.1.0] - 2024-02-01\n### Added\n- feature A\n";
+        let new_entry = "## [0.2.0] - 2024-03-01\n### Added\n- feature B\n";
+        let result = insert_changelog_entry(existing, new_entry);
+
+        let pos_new = result.find("## [0.2.0]").unwrap();
+        let pos_old = result.find("## [0.1.0]").unwrap();
+        assert!(pos_new < pos_old, "new version should be before old version");
+    }
+}