Improve tweak generation status and timeouts

[jamesrochabrun]

Summary

• replace the fixed three-minute tweak-agent deadline with a five-minute inactivity timeout that resets when the agent makes progress
• show a single generation banner with a persistent elapsed timer
• make tweak-agent, conflict, and defaults-save errors dismissible
• keep Canvas unchanged by routing status presentation through the Easel wrapper

Why

Long-running Codex tweak generations could be cancelled at exactly three minutes even while the agent was actively working. The panel also duplicated loading indicators, restarted its timer whenever the popover reopened, and left terminal errors with no dismissal path.

Impact

High-quality generations can continue beyond three minutes as long as they are progressing, while genuinely stalled tasks are still cancelled. Users get one stable progress surface and can dismiss every terminal status.

Validation

• xcodebuild -project Easel.xcodeproj -scheme EaselChat-Package -configuration Debug -destination 'platform=macOS' build -quiet
• focused EaselWebInspector timer and status routing tests (6 tests passed)
• timeout tracker unit tests added under EaselChatTests

Direct swift test for EaselChat remains blocked by the existing CodeEditSymbols resource packaging issue involving Bundle.module; the Xcode package build succeeds.