v0.2.3 - Complete Chatify install paths and docs

Completes the rename across installer and documentation paths. The shared installer now pins this renamed release instead of the old CustomChat archive. README links open current Chatify documentation; release docs no longer say unpublished. Historical migration notes now show the explicit distribution command.

Run:

uvx --from chatify-app chatify start

Do not use bare uvx chatify: that distribution belongs to a different project.

Checks: 796 unit tests passed (one skipped), eight Linux installer scenarios passed, and 24 mobile/desktop automated accessibility cases passed with no detected WCAG A/AA violations or horizontal document overflow. These checks are not a manual screen-reader audit or a live model-provider test.