version: mark CoderAI 0.1.0 and surface it in the admin web UI

Add a canonical codai.__version__ = "0.1.0" as the single source of truth (kept
separate from Config.version, which is the config-schema/migration version). The
admin template renderer injects it as coderai_version, and base.html shows it as a
small "v0.1.0" pill next to the CoderAI logo on every page.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>