Migrate chat log to JSONL format
Server changes:
- format/block.go: Block struct with JSONL marshaling, RenderBlock for text
- Deleted format/event.go, format.go, format_test.go (old delimiter format)
- agent/chat.go: Dual logs (rawLog JSONL + textLog rendered text)
- agent/chatlog.go: Streaming via flushPartial/closeBlock, skip internal events
- fs/spec.go: New files log.raw (JSONL), log (text), block (ID lookup)
- Removed chat/chat.raw/chat.search from namespace
GUI changes:
- chatblockmodel: JSONL parsing via QJsonDocument, removed regex state machine
- ollie9pclient: Read from log.raw for replay, removed old streaming code
- Added Context type to block enum, filter context/state/usage from display
Docs updated: AGENTS.md, system_prompt.md, architecture-*.md, scripts/o
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