chore(db): renumber the custom-block trace migration around a 0299 collision

Staging landed its own 0299 (`table_run_dispatches.heartbeat_at`) while this
branch was open. The two migrations are independent — different tables, no shared
statement — so only the number and drizzle's snapshot chain collided.

Regenerated rather than hand-merged: a drizzle snapshot is a full-schema dump
whose `prevId` links it to its parent, so editing one by hand to sit after a
migration it was not generated against is how the chain silently stops matching
the database. Staging's 0299 and its snapshot are taken verbatim; this is 0300,
generated against them, and its SQL is byte-identical to what it replaced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: icecrasher321

packages/db/migrations/0300_hesitant_war_machine.sql

@@ -0,0 +1 @@
+ALTER TABLE "custom_block" ADD COLUMN "trace_child_runs" boolean DEFAULT false NOT NULL;