fix: lazy TextEncoderAPI client with retry + HTTP readiness gate

Fix text encoder payload parsing and add remote encoder switch

Improve error extraction: collect all error strings from text encoder response

Debug: print full traceback on text encoder init failure to expose real error

Improve text encoder error messages: better diagnostics for HF token issues

Improve text encoder API error detection: validate .npy paths and detect error messages

Fix generate notification: reuse persistent notification and properly transition to error state

Use lazy TextEncoderAPI client in API-only mode (no startup fallback)

Add core kimodo package modules required by native demo