Decompose App.tsx phase 2 step 4: extract useServerCommands #2155

Step 4 of phase 2 of the App.tsx decomposition — see #2129 for the phase, #2126 for the whole effort.

This is a stacked PR. Its branch is cut from step 3's and its PR targets that branch, not v2/main. Do not land it before step 3.

Scope — useServerCommands(session, oauth, stores), ~530 lines

• onCallTool, onClearToolResult, onToolsUiChange
• onGetPrompt, onReadResource, onReadResourceContents, onSubscribeResource, onUnsubscribeResource, onCompleteArgument
• onCancelTask, onCancelToolCall, onClearCompletedTasks, onSetLogLevel, onSetModernLogLevel
• the refresh and load-more callbacks
• onTogglePaginatedLists (~135 lines on its own)
• toolCallState, getPromptState, readResourceState

Every one of these routes through runWithCommandAuthRecovery from step 2. That wrapper is the reason this cluster cannot precede the OAuth one.

Constraints carried from #2129

• ⚠️ Bug: the pagination toggle shows the stale entry's value after switching servers and back #2095's pagination-toggle behavior lives in onTogglePaginatedLists / paginatedListsOverride. Do not change it here. Land the move inert; anything further goes on top, because a behavior change buried in a 135-line relocation is unreviewable.
• No behavior change.

Done when

• useServerCommands is its own hook
• ≥90% on all four coverage dimensions
• npm run ci green, all three web smokes included