Schema, Workers, and Build Log Overhaul

Refactored the digest worker by extracting singletons and post-exchange hooks into dedicated modules, and consolidating cron/drift pipelines into a helper function.

Updated the chat history retrieval to read exclusively from SQLite using SQL-level pagination via get_paginated_history_durable(), replacing the unreliable in-memory MemoryStore.

Promoted several silent debug catches to error level to ensure failures are visible during operation.

Refined the database schema by making Migration 009 a no-op and adding four composite indexes on hot query paths.

Replaced the build log logic, moving the full pipeline to n8n, making GitHub Actions a simple trigger that POSTs to an n8n webhook.

Switched the build-log webhook to asynchronous mode to prevent Cloudflare timeouts when processing long-running Ollama calls.

Updated webhook authentication to use opaque URL tokens for greater reliability through proxies, deprecating the need for X-Webhook-Secret headers for some flows, though others remain required.

Improved build log state tracking by switching from a potentially unreliable commit-count comparison to a hash-based state file stored in the web directory.

• Read chat history directly from SQLite instead of MemoryStore.

• Extracted digest worker singletons and hooks for modularity.

• Migrated build log processing pipeline to n8n/Ollama.

• Switched build-log state detection to use hash-based state files.

• Added four composite indexes on hot query paths.

• Staggered webhook fires with a 5s delay to prevent Ollama overload.