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/overview.rs

@@ -108,7 +108,7 @@ fn find_story_name(root: &std::path::Path, num_str: &str) -> Option<String> {
         "6_archived",
     ];
     for stage in &stages {
-        let dir = root.join(".story_kit").join("work").join(stage);
+        let dir = root.join(".storkit").join("work").join(stage);
         if !dir.exists() {
             continue;
         }