feat(knowledge): fold the Connectors view into Manage as a tab — both are knowledge sources #16897

What

/knowledge/connectors and /knowledge/manage are two top-level entries in the Knowledge sidebar, and they are the same thing: both are how a data source gets into the knowledge base. Connectors ingest from an external system, Upload and Watch Folders ingest from files. Splitting them puts "how do I get data in" in two places, and the sidebar implies they are different kinds of work.

Manage should be the single answer to "give the knowledge base a data source".

Current shape

/knowledge/manage already is a tabbed surface. KnowledgeEntries.vue carries ManageTab = 'upload' | 'manage' | 'watchFolders', driven by ?tab= so a deep link opens on the right tab:

// Manage tab state — initialized from ?tab= so /knowledge/manage?tab=watchFolders
// (the redirect target for the retired /knowledge/watch-folders route) opens
// directly on the right tab.

The pattern is already established. /knowledge/watch-folders was a sibling route and was retired into ?tab=watchFolders, with the old path kept as a redirect (router/index.ts:376). Connectors is the same move, one route later.

/knowledge/connectors (router/index.ts:257) renders components/knowledge/connectors/ConnectorManager.vue and has its own sidebar entry in views/KnowledgeView.vue:160.

Acceptance criteria

• ConnectorManager renders as a tab inside /knowledge/manage, alongside Upload, Manage and Watch Folders.
• /knowledge/connectors redirects to /knowledge/manage?tab=connectors, so existing links and bookmarks keep working — the same treatment /knowledge/watch-folders got, not a deletion.
• The separate Connectors entry is gone from the Knowledge sidebar; Manage is the single entry for adding a data source.
• The tab label is an i18n key present in all 11 locales, not a hardcoded string.
• ?tab=connectors opens directly on that tab, as ?tab=watchFolders does.

Not in scope

The connector functionality is unchanged — this is where it lives, not what it does. ConnectorManager.vue is moved, not rewritten.