feat(sidebar): add show_kanban_sessions toggle to hide kanban worker sessions (#6780)

* feat(sidebar): add show_kanban_sessions toggle to hide kanban worker sessions

* fix(sidebar): kanban source-filter override + filtered-view cap (cron/webhook parity)

Gate re-review (Codex) found the kanban-hide addition missed cron/webhook
parity for the source-filter case:
- An explicit kanban source_filter now overrides the default hide (threaded
  source_filter into _dedupe_cli_sidebar_sessions_for_api, normalized with
  strip().lower() to match the loader), so a deliberate kanban view shows
  those rows even with the toggle off. Scoped to the matching source only.
- A dedicated KANBAN_PROJECT_CHIP_LIMIT bounds a filtered kanban-only view,
  mirroring CRON/WEBHOOK_PROJECT_CHIP_LIMIT.

Deliberately NOT changing the general exclude_sources: the original PR lets
kanban load on the source_filter=None path so the toggle-ON case works (the
hide is applied by _hide_from_default_sidebar only when the toggle is off).
Excluding kanban there would save the 20-row budget but break toggle-on
unless a bounded kanban merge is added (cron/webhook don't do that either) —
that query-budget optimization is deferred as a separate cross-cutting change.
The pinned-survives-hide finding is also out of scope (cron/webhook hide pinned
identically, confirmed by Codex). Adds bite-tested regressions.

Co-authored-by: vduke <vduke@users.noreply.github.com>

---------

Co-authored-by: nesquena-hermes <nesquena-hermes@users.noreply.github.com>

api/config.py

@@ -9276,6 +9276,7 @@ _SETTINGS_DEFAULTS = {
     "show_claude_code_sessions": True,  # allow filtering Claude Code rows without hiding other imported sources
     "show_cron_sessions": False,  # surface cron sessions in the sidebar (subordinate to show_cli_sessions)
     "show_webhook_sessions": False,  # surface webhook sessions in the sidebar (subordinate to show_cli_sessions)
+    "show_kanban_sessions": False,  # surface kanban worker sessions in the sidebar (subordinate to show_cli_sessions)
     "show_previous_messaging_sessions": False,  # show older Telegram/Discord/etc. reset segments
     "sync_to_insights": False,  # mirror WebUI token usage to state.db for /insights
     "check_for_updates": True,  # check if webui/agent repos are behind upstream
@@ -9620,6 +9621,7 @@ _SETTINGS_BOOL_KEYS = {
     "show_claude_code_sessions",
     "show_cron_sessions",
     "show_webhook_sessions",
+    "show_kanban_sessions",
     "show_previous_messaging_sessions",
     "sync_to_insights",
     "check_for_updates",