adventure: count the treasures an adventurer has actually found

A treasure_found fact turns loot into a trophy: a story-grade find lands on the
who page as a stat tile, a named row in a Treasures found showcase, and a trail
entry linking back to the dispatch. A realm-first hoard rides the priority tier
the way zone_first does, and gets the same star and callout.

The item name travels in the fact's stakes field, which the events log now keeps
(a new nullable column, backfilled to NULL for older rows). Counting is only ever
from the fact, never the vault snapshot, so a bought sword is never a trophy and a
history that predates the fact is a clean zero.

This is a new event_type, so Pete's ingest must be deployed before gogobee emits
one, or the first finds park forever on the retry ladder.

internal/storage/db.go

@@ -101,6 +101,10 @@ func runMigrations(d *sql.DB) error {
 	// click-through page. Rides the roster snapshot; NULL on rows pushed by a
 	// gogobee build that predates the detail page.
 	addColumnIfMissing(d, "adventure_roster", "detail_json", "TEXT")
+	// The noun a fact is about (a mischief bounty, a found treasure's name). Facts
+	// recorded before the treasure_found event existed carry NULL, which is right:
+	// they had no such noun to keep.
+	addColumnIfMissing(d, "adventure_events", "stakes", "TEXT")
 
 	// FTS5 virtual tables don't support IF NOT EXISTS reliably.
 	// Check sqlite_master before creating.