feat: miller column browser, offline cache, search, breadcrumbs

- Dynamic miller column sizing with flexbox layout
- Root column (160px), middle slices (48px), active column (flex)
- Auto-scroll browser to rightmost column on navigation
- Offline indicator UI and IndexedDB cache integration
- /api/documents endpoint for client-side document caching
- Breadcrumb navigation in document content area
- FTS5 search with SQLite virtual table
- Client-side Mermaid and KaTeX rendering via CDN
- Deep sample content (advanced-topics/raft-deep-dive)
- Border removal (only search button keeps radius)
- Full viewport layout with proper borders between sidebar/content

content/math-test.md

@@ -0,0 +1,31 @@
+# Math and Diagrams Test
+
+This page tests client-side rendering of Mermaid diagrams and KaTeX math.
+
+## Mermaid Diagram
+
+```mermaid
+flowchart TD
+    A[Start] --> B{Is it?}
+    B -->|Yes| C[OK]
+    B -->|No| D[End]
+```
+
+## Inline Math
+
+The quadratic formula is $x = {-b \pm \sqrt{b^2-4ac} \over 2a}$.
+
+## Block Math
+
+$$
+\int_0^\infty e^{-x^2} dx = \frac{\sqrt{\pi}}{2}
+$$
+
+## Another Diagram
+
+```mermaid
+graph LR
+    A[Client] --> B[Server]
+    B --> C[Database]
+    B --> D[File System]
+```