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>

.gitignore

@@ -5,9 +5,9 @@
 # Local environment (secrets)
 .env
 
-# App specific (root-level; story-kit subdirectory patterns live in .story_kit/.gitignore)
+# App specific (root-level; story-kit subdirectory patterns live in .storkit/.gitignore)
 store.json
-.story_kit_port
+.storkit_port
 
 # Rust stuff
 target