chore(db): schema.go searches three levels up — replaces the tests-dir symlink

Host-side test runs use CWD=cmd/server/tests, three levels below the repo
root; the location search only went up two, so it never found
database/schema/schema.sql from there and init() fatal-exited. That gap
was being papered over by an untracked local symlink
(cmd/server/tests/database -> ../../../database) hidden behind a bare
`database` line in .git/info/exclude — which also broke `git add` under
database/. Fix the search list instead and drop the filesystem trick:
no symlink to commit, no exclude hack, works on any platform.

Verified: contract pins green from cmd/server/tests with no symlink
present (init resolves via the new entry); parse test green.

internal/database/schema.go

@@ -25,6 +25,9 @@ func init() {
 		"/app/database/schema/schema.sql",
 		"../database/schema/schema.sql",
 		"../../database/schema/schema.sql",
+		// Integration tests run with CWD=cmd/server/tests, three levels
+		// below the repo root — two up only reaches cmd/.
+		"../../../database/schema/schema.sql",
 	}
 
 	var content []byte