Generate no lookup conf for an unnamed variable

[nandanrao]

name is both the output variable name and the key into the ad's frozen
ad_attributions row, so a lookup conf without one reads nothing off the row
while presenting itself in the form as configured — a filled-in row that can
only ever yield nothing.

The guard was variables.length === 0, which one unnamed variable passes: its
length is 1.

-  if (source !== FLY_SOURCE || variables.length === 0) return [blankConf()];
-  return variables.map(lookupConf);
+  if (source !== FLY_SOURCE) return [blankConf()];
+  const named = variables.filter(name => !!name);
+  return named.length ? named.map(lookupConf) : [blankConf()];

Also pins two ref_mode properties that held but were untested: a conf stating
an explicit mode keeps it through an unrelated edit, and a mode matching what
was loaded does not warn.

Provenance. Found by comparing what shipped in #247 against
feature/ref-mode-dashboard-ux (#246), which built the same design
independently and carries generateLookupConfs.test.ts covering this case. An
AST-level comparison showed adopt and swoosh are behaviourally identical between
the two implementations — events.go byte-identical, and the only differences
in study_conf.py / marketing.py / csv_export.py are one variable rename,
one tightened optional parameter, and one error-message wording. This was the
one real gap.

Both new generateLookupConfs tests fail without the fix.

npx tsc --noEmit        clean
CI=true npx craco test  170 passed, 15 suites  (was 166)
CI=true npx craco build Compiled successfully

Dashboard only — Netlify deploys from main on merge.

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