rename .story_kit directory to .storkit and update all references

Renames the config directory and updates 514 references across 42 Rust
source files, plus CLAUDE.md, .gitignore, Makefile, script/release,
and .mcp.json files. All 1205 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/matrix/commands/show.rs

@@ -34,7 +34,7 @@ pub(super) fn handle_show(ctx: &CommandContext) -> Option<String> {
     for stage in &stages {
         let dir = ctx
             .project_root
-            .join(".story_kit")
+            .join(".storkit")
             .join("work")
             .join(stage);
         if !dir.exists() {
@@ -92,7 +92,7 @@ mod tests {
     }
 
     fn write_story_file(root: &std::path::Path, stage: &str, filename: &str, content: &str) {
-        let dir = root.join(".story_kit/work").join(stage);
+        let dir = root.join(".storkit/work").join(stage);
         std::fs::create_dir_all(&dir).unwrap();
         std::fs::write(dir.join(filename), content).unwrap();
     }