fix(KB): blank-screen on panel open + tooltips on bulk-action buttons

The Stored Knowledge Base Files render crashed on first open in v1.32.0-rc.5
with `ReferenceError: sourceToDisplayName is not defined`. The table column's
render() called `sourceToDisplayName(record.source)` but the function was
extracted to `lib/kb_file_grouping.ts` in PR #892 and never imported in
KnowledgeBaseModal.tsx. The unhandled error unmounts the entire React tree,
so users see a blank screen ~20s after opening the panel.

Root cause: PR #895 (conditional warnings) rewrote the render() and used
`sourceToDisplayName(record.source)` instead of `record.displayName`, which
KbFileGroup already carries from groupAndSortKbFiles(). PR #895's review
follow-up (cbae48a) compounded this by narrowing the StyledTable generic
from `KbFileGroup` to `{source: string}`, hiding the type drift from tsc.

This restores the post-#892 pattern:
- StyledTable generic back to `KbFileGroup`
- Render uses `record.displayName` (works for both per-file rows and the
  collapsed admin-docs row; calling sourceToDisplayName on the synthetic
  `__admin_docs_group__` would have rendered that literal as the row name).

Also folds in tooltip copy on the three bulk-action buttons (Reset & Rebuild,
Re-embed All, Sync Storage) so the difference in destructiveness is visible
on hover. Uses native `title` attribute via StyledButton's prop pass-through;
no new component dependency.

Inertia tsconfig catches this regression cleanly (TS2304 + TS2339); the
pre-push hook only runs the backend tsconfig which excludes inertia/**, so
the bug shipped. Tracking the typecheck-coverage gap as a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

admin/inertia/components/chat/KnowledgeBaseModal.tsx

@@ -420,6 +420,7 @@ export default function KnowledgeBaseModal({ aiAssistantName = "AI Assistant", o
                   onClick={() => { setResetTyped(''); setBulkMode('reset') }}
                   disabled={isUploading || qdrantOffline || bulkBusy}
                   loading={resetMutation.isPending}
+                  title="Drop the entire embeddings collection and re-embed everything from scratch. Permanently removes vectors for files no longer on disk. Destructive: requires typing RESET to confirm."
                 >
                   Reset & Rebuild
                 </StyledButton>
@@ -430,6 +431,7 @@ export default function KnowledgeBaseModal({ aiAssistantName = "AI Assistant", o
                   onClick={() => setBulkMode('reembed')}
                   disabled={isUploading || qdrantOffline || bulkBusy || storedFiles.length === 0}
                   loading={reembedMutation.isPending}
+                  title="Re-embed every file on disk, replacing existing vectors file-by-file. Vectors for files no longer on disk are preserved. Use this if the chunker or embedding model has changed."
                 >
                   Re-embed All
                 </StyledButton>
@@ -440,6 +442,7 @@ export default function KnowledgeBaseModal({ aiAssistantName = "AI Assistant", o
                   onClick={handleConfirmSync}
                   disabled={syncMutation.isPending || isUploading || qdrantOffline || bulkBusy}
                   loading={syncMutation.isPending || isUploading}
+                  title="Scan storage for new files and queue any that haven't been embedded yet. Safe to run anytime; won't touch already-embedded content."
                 >
                   Sync Storage
                 </StyledButton>
@@ -454,7 +457,7 @@ export default function KnowledgeBaseModal({ aiAssistantName = "AI Assistant", o
                 </span>
               </div>
             )}
-            <StyledTable<{ source: string }>
+            <StyledTable<KbFileGroup>
               className="font-semibold"
               rowLines={true}
               columns={[
@@ -466,7 +469,7 @@ export default function KnowledgeBaseModal({ aiAssistantName = "AI Assistant", o
                     return (
                       <div className="flex flex-col gap-1">
                         <span className="text-text-primary">
-                          {sourceToDisplayName(record.source)}
+                          {record.displayName}
                         </span>
                         {warnings.map((w, i) => (
                           <span