etl: add Share handler

[raymondjacobson]

Share handler records content shares (track/playlist/album). Unlike
Save/Repost, shares allow duplicates and have no Unshare counterpart.

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

[raymondjacobson]

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• etl: make all migrations idempotent #196
• etl: add parity test tooling (snapshot/diff) #191
• etl: add AssociatedWallet Create/Delete handlers #190
• etl: add Tip reaction handler #189
• etl: add DashboardWalletUser Create/Delete handlers #188
• etl: add EncryptedEmail and EmailAccess handlers #187
• etl: add Event Create/Update/Delete handlers #186
• etl: add Track Download handler #185
• etl: add Share handler #184 👈 (View in Graphite)
• etl: add Subscribe/Unsubscribe handlers #183
• etl: fix social handler dispatch to use wildcard entity type matching #182
• etl: add Comment handlers (Create/Update/Delete/React/Unreact/Pin/Unpin/Report/Mute/Unmute) #180
• etl: add Notification Create/View and PlaylistSeen View handlers #179
• etl: add MutedUser Mute/Unmute handlers #178
• etl: add Playlist, Social, DeveloperApp, Grant handlers #177
• etl: add Track Create/Update/Delete handlers (genre allowlist, slug collision, routes) #176
• etl: add User Verify handler (0003 migration, verified_address) #150
• etl: add User Update handler (markNotCurrent, metadata merge) #149
• Add User Create entity manager handler #148
• Add entity manager foundation for ETL indexer #147
• main

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[raymondjacobson]

Superseded by #200 (squash merged)