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/raft-deep-dive/index.md

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+# Raft Deep Dive
+
+A detailed look at the Raft consensus algorithm.
+
+## How Raft Works
+
+Raft uses a leader-follower model where one node is elected as the leader and all other nodes are followers.
+
+## Key Components
+
+1. Leader Election
+2. Log Replication
+3. Safety
+
+## Election Process
+
+When a follower doesn't hear from the leader for a timeout period, it increments its term and starts an election.
+
+```mermaid
+graph TD
+    A[Follower] --timeout--> B[Candidate]
+    B --votes received--> C[Leader]
+    C --heartbeat--> A
+```
+
+## State Machine
+
+The state machine applies committed log entries to produce the same output on all nodes.