Add durable loop task memory synthesis

[nathanwhitbot]

Summary

• add task-scoped durable loop memory snapshots with compact objective, decisions, blockers, recurring themes, and PR/artifact state
• project task.memory_updated events into task snapshots and include them in ledger/event reads used by loop workers and replanning
• render synthesized memory in durable-loop worker prompts ahead of the fixed-size context ledger
• add focused synthesis/projection/prompt tests plus service-level coverage that a later loop iteration receives synthesized memory

Validation

• go test ./internal/orchestrator -run 'TestServiceRunsDurableLoopModeWithoutBrainPlanning|TestSynthesizeLoopTaskMemory|TestLoopTaskMemory|TestDurableLoopPrompt' -count=1
• go test ./internal/orchestrator ./internal/eventstore ./internal/core -count=1
• go test ./... -count=1

[nathanwhit]

Reviewed durable-loop task memory synthesis. The event projection, ledger query expansion, refresh cadence, important-event triggers, prompt rendering, and payload bounding are covered by focused tests, and the durable-loop prompt refreshes from latest task state before each iteration. CI is green.