chore: update openspec config and gitignore

Add claude_slash_commands and parallel_tasks settings to openspec
config. Extend gitignore for vector-search db variants. Fix missing
trailing newline in plugin-dir-structure spec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: retsohuang

.gitignore

@@ -29,3 +29,4 @@ build/
 *.log
 .spectra/
 openspec/.vector-search.db
+openspec/.vector-search.db*

openspec/config.yaml

@@ -1,4 +1,6 @@
 schema: spec-driven
+claude_slash_commands: false
+parallel_tasks: true
 
 # Project context (optional)
 # This is shown to AI when creating artifacts.

openspec/specs/plugin-dir-structure/spec.md

@@ -61,4 +61,4 @@ code:
   - plugins/github-tools/.claude-plugin/plugin.json
   - plugins/worktree-bootstrap/hooks/hooks.json
   - plugins/worktree-bootstrap/skills/config/SKILL.md
--->
+-->