fix(obsidian): preserve trace identity during title edits

[Fail-Safe]

Summary

• Add an explicit Edit trace title command that updates semantic title metadata through MCP without changing stable trace IDs.
• Restore canonical filenames after external renames; avoid duplicate auto-onboarding and preserve existing canonical files.
• Prepare Noema v0.21.7 with Obsidian plugin v0.5.2. Existing merged continuity improvements remain included; local experimental changes are excluded.

Validation

• Full serial make test: formatting, strict Clippy, 215 Rust unit tests and integration suites passed.
• All 59 continuity benchmark mechanics tests passed.
• Obsidian: 6 tests, production build, TypeScript checking, and committed bundle parity passed.
• Hermes compatibility: 103 tests passed.
• Optimized host build and version smoke passed. The Makefile copy step needed the explicit shared target-directory path.
• Isolated live MCP and watcher smoke passed: semantic title update, unchanged body and ID, canonical filename restoration, and no duplicate trace.
• Desktop Obsidian UI clicking was not re-exercised in this release pass; plugin protocol tests and the live server/watcher path were verified separately.

No private benchmark corpus or reports are included.