Simplify after review: dedupe, trim comments, flatten conditionals

• Extract addPruneCandidates helper; the prune-managed switch is no longer pasted into both BuildPlans and BuildReplicationPlans.
• Extract syncSession.finalizeCounts; the applyRejections + counter loop block is no longer duplicated between runSync and runReplicate.
• Use convert.DesiredRefsForPlans in the bootstrap tail phase instead of building gitproto.DesiredRef inline.
• Drop the defensive pushed < 0 clamp in bootstrapWithInputs; if Pushed and Warned ever disagreed, masking it would hide the bug.
• Fold the "AllRefs implies BestEffort" coupling into allRefsFlag via cobra PreRunE instead of pasting the if-statement into two RunE bodies.
• Flatten the 3-level nested conditional in NormalizeMapping.
• Trim verbose doc blocks: RefKind, ActionWarn, RefScope.AllRefs, SyncPolicy.BestEffort, Pusher.OnRejection, syncSession.rejections, the bootstrap tail-phase comment, and the test docstrings that narrated motivation rather than the assertion. Removes the two empty-branch comments in the count switches by collapsing ActionWarn/Skip/Block into one no-op branch.

Net: -89 lines, all 8 AllRefs integration + smoke tests still pass.