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/commands/changelog.rs

@@ -7,6 +7,7 @@ use std::path::PathBuf;
 
 use crate::config::{Language, manager::ConfigManager};
 use crate::generator::ContentGenerator;
+use crate::git::GitRepo;
 use crate::git::find_repo;
 use crate::git::{CommitInfo, changelog::*};
 use crate::i18n::{Messages, translate_changelog_category};
@@ -120,7 +121,10 @@ impl ChangelogCommand {
 
         // Get commits
         println!("{}", messages.fetching_commits());
-        let commits = generate_from_history(&repo, self.from.as_deref(), Some(&self.to))?;
+
+        // Determine from_tag: use explicit --from, or auto-detect from changelog
+        let from_tag = self.resolve_from_tag(&repo, &output_path, &messages);
+        let commits = generate_from_history(&repo, from_tag.as_deref(), Some(&self.to))?;
 
         if commits.is_empty() {
             bail!("{}", messages.no_commits_found());
@@ -167,33 +171,13 @@ impl ChangelogCommand {
             }
         }
 
-        // Write to file (always prepend to preserve history)
+        // Write to file (always prepend new entry before existing versions)
         if output_path.exists() {
             let existing = std::fs::read_to_string(&output_path)?;
             let new_content = if existing.is_empty() {
                 format!("{}{}", CHANGELOG_HEADER, changelog)
-            } else if existing.starts_with(CHANGELOG_HEADER) {
-                format!("{}{}", CHANGELOG_HEADER, changelog)
-            } else if existing.starts_with("# Changelog") {
-                let lines: Vec<&str> = existing.lines().collect();
-                let mut header_end = 0;
-
-                for (i, line) in lines.iter().enumerate() {
-                    if i == 0 && line.starts_with('#') {
-                        header_end = i + 1;
-                    } else if line.trim().is_empty() {
-                        header_end = i + 1;
-                    } else {
-                        break;
-                    }
-                }
-
-                let header = lines[..header_end].join("\n");
-                let rest = lines[header_end..].join("\n");
-
-                format!("{}\n{}\n{}", header, changelog, rest)
             } else {
-                format!("{}{}", CHANGELOG_HEADER, changelog)
+                insert_changelog_entry(&existing, &changelog)
             };
             std::fs::write(&output_path, new_content)?;
         } else {
@@ -206,6 +190,28 @@ impl ChangelogCommand {
         Ok(())
     }
 
+    fn resolve_from_tag(
+        &self,
+        repo: &GitRepo,
+        output_path: &PathBuf,
+        messages: &Messages,
+    ) -> Option<String> {
+        // Explicit --from always wins
+        if self.from.is_some() {
+            return self.from.clone();
+        }
+
+        // Auto-detect: find highest version already in changelog
+        let existing = std::fs::read_to_string(output_path).ok()?;
+        let versions = parse_changelog_versions(&existing);
+        let highest = versions.first()?;
+
+        // Match highest version to a git tag
+        let tag = repo.find_tag_by_version(highest)?;
+        println!("  {}: {}", messages.version(), tag.name);
+        Some(tag.name)
+    }
+
     async fn generate_with_ai(
         &self,
         version: &str,