Dreaming (optional memory consolidation)

Opt-in background pass that finds related memories (via dreaming.relatedThreshold, default 0.75, independent of deduplicationSimilarityThreshold), asks the configured opencodeProvider / opencodeModel to merge, update, supersede, keep, or flag contradictions, and soft-deletes superseded rows into recoverable trash. Pinned memories are never touched. Set dreaming.crossProject: true (or memory.defaultScope: "all-projects") to group across project tags; user-scope stays separate. Configure under dreaming in opencode-mem.jsonc (enabled default false). The web UI exposes Trash (restore) and Dream (manual run). Soft-deleted rows are hard-purged after dreaming.trashRetentionDays during normal cleanup.

Deeper related-threshold dreaming (update/supersede/flag, cross-project) lands in the follow-up PR for #464.