docs: replace ASCII diagrams and clarify fallback config

[camaragon]

Why change

Replace remaining docs ASCII diagrams with supported Mermaid and clarify fallback configuration without losing legacy compatibility guidance.

Files changed

• cron-script-only.md: replace the no-agent execution diagram with Mermaid.
• kanban.md: replace the GUI architecture diagram with Mermaid and show the actual DB persistence -> FastAPI/WebSocket tail -> React UI boundary.
• providers.md: clarify that fallback routing has no environment variables, preserve legacy fallback_model compatibility, and recommend fallback_providers for new configuration.

Verification run

• full Docusaurus build — passed for English and zh-Hans
• full ASCII guard — passed
• touched-file ASCII guard — passed
• git diff --check — passed

Risk level

Low. Docs-only changes; no runtime code or dependency changes.

[teknium1]

Thanks for the focused documentation cleanup. One correction is needed during salvage.

Problems

• website/docs/user-guide/features/kanban.md:511 changes the architecture to DB --> UI, but live updates are delivered by the FastAPI /events WebSocket, which tails task_events (plugins/kanban/dashboard/plugin_api.py:10-11, :2379). The previous diagram named that WebSocket path; the Mermaid replacement drops it.

Suggested changes

• Route the live-update edge through the API/router to the UI and label it as the WebSocket tail of task_events; keep the DB as the persistence/write target.
• Preserve the legacy fallback_model compatibility note when reconciling the fallback documentation (hermes_cli/fallback_config.py:51-64).

Automated hermes-sweeper review.

[camaragon]

Refreshed onto current main and addressed all review threads in c3a6921c8d.

Current scope:

• replace two remaining ASCII diagrams with Mermaid
• model Kanban live updates accurately through FastAPI/WebSocket tailing persisted task_events
• document no fallback environment variables and preserve the legacy fallback_model compatibility note
• drop stale/out-of-scope edits already superseded on current main

Verification:

• full Docusaurus build: passed for English and zh-Hans
• full ASCII guard: passed
• touched-file ASCII guard: passed
• git diff --check: passed

[camaragon]

Refreshed onto current main at 6ac541a6db. Fresh local verification: full diagram lint passed; full Docusaurus build generated both locales successfully; no broken-link warning originated from the three touched source pages; git diff --check passed. The prior Kanban WebSocket-boundary review request remains addressed and no unresolved review threads remain. Fresh GitHub CI is running on the new head.