Document shared delivery-mode channel table pattern in LESSONS.md

[mapgie]

Summary

• Adds lesson Add Supabase schema.sql and setup docs for new installs #29 to LESSONS.md, capturing the notification-channel consolidation from Give overdue-chore alerts the same Alarm/Notification/Silent + DND wiring as tasks #89: when a new feature (overdue-chore alerts) needed the same Alarm/Notification/Silent + DND-bypass treatment as an existing one (task/reminder alerts), the transferable lesson is to model it as one ReminderKind x ChannelStyle table that every caller resolves through, rather than copy-pasting a second parallel channelForDeliveryMode()-style function and a second hand-written channel-creation block that can drift out of sync with the first.

No app code changes; LESSONS.md isn't one of the file types that requires a changelog fragment per this repo's conventions.

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[mapgie]

Heads-up on a LESSONS.md numbering collision. PR #92 fixes a pre-existing duplicate ## 27 (two lessons shared it on main) via a cascade renumber, which moves the surfaces lesson to #29 and adds a new #30. This PR currently adds the notification-channel lesson as #29, so the two will conflict at the tail of LESSONS.md.

Suggested resolution: let #92 merge first, then rebase this PR and renumber this lesson to ## 31 (after #92's #30). Target ordering ends up: 27 warn-discard, 28 theme-builder, 29 surfaces, 30 accent-CompositionLocal, 31 delivery-mode channel table.

(Underlying point: sequential hand-numbered lessons keep colliding across concurrent PRs, the same problem the changelog fragment system was built to avoid. Worth considering dropping the numbers entirely, but that's a separate change.)

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Generated by Claude Code