fix: align compaction toggle with detector for proxy providers (#658)

* fix: align compaction toggle with detector for proxy providers (AIHubMix)

The compaction detector uses provider-agnostic model ID lookup
(getModelContextWindowSync) which finds context windows across all
providers, while the UI toggle only used provider-specific lookup
(getProviderModelContextWindowSync) which returns null for proxy
providers like AIHubMix not in the registry.

This caused auto-compression to trigger silently while the toggle
was disabled (greyed out), preventing users from controlling it.

Add the same provider-agnostic fallback to both contextWindowKnown
and effectiveContextWindow so the UI is consistent with the detector.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: add provider-agnostic context window fallback in task page

Same inconsistency as InputBox — task page only used provider-specific
lookup for context window, causing token percentage to not display for
proxy providers like AIHubMix.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: include modelRegistryVersion in useMemo deps for context window

The useMemo for contextWindowKnown and effectiveContextWindow called
getModelContextWindowSync/getProviderModelContextWindowSync but didn't
depend on the registry version. After async registry refresh, these
memos could return stale values even though a rerender was triggered.

Capture useModelRegistryVersion() return value and add it to deps.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>