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/advanced-topics/distributed-systems/consensus-algorithms/index.md

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+# Consensus Algorithms
+
+Algorithms for achieving agreement in distributed systems.
+
+## Overview
+
+Consensus algorithms ensure that a group of nodes agree on a single value or state, even in the presence of failures.
+
+## Popular Algorithms
+
+- Raft
+- Paxos
+- Practical Byzantine Fault Tolerance (PBFT)