feat(obsidian): show trace tiers in file explorer

[Fail-Safe]

Summary

• annotate native File Explorer trace rows with theme-aware short, mid, and long tier badges from cached frontmatter
• add a persisted, default-on setting that hides or restores badges immediately
• bump the Obsidian plugin and MCP client metadata to 0.4.0 and update the generated bundle and documentation

Validation

• npm test
• npm run build
• npx tsc --noEmit
• cargo test plugin:: --locked
• make test
• repeat production build produced an identical bundle hash
• deployed plugin payload hashes matched the checkout and live visual placement was confirmed

The first full make test run hit a transient temporary mutation-lock contention in one recovery test. That exact test passed on immediate isolated retry, and the complete default-parallel make test rerun passed.