Kill the count/mean aggregation vocabulary everywhere above the compiler

From the 8/13 data weekly. The target compiler already enforces sum-only — SUPPORTED_LEDGER_AGGREGATIONS = frozenset(("sum",)) (packages/microcosm-build/src/microcosm/build/ledger_targets.py:22), with the single declared time_mean carve-out for facts Chronicle asserts are means over time. Counts are sums of indicator/person-count variables; there are no mean targets.

But the count/mean vocabulary keeps resurfacing in layers ABOVE the compiler and has confused the team repeatedly ("we were stuck on this a lot" — María). Known survivals:

• the calibration dashboard's target card shows an "aggregation: sum" field as if count/mean were live alternatives (Anthony removing);
• "source concept" / "measure concept" fields — terminology from the count-era target construction (María traced the lineage in the meeting);
• any remaining count/mean branches or labels in Chronicle→target compilation helpers and their tests.

Definition of done: grep-clean above the compiler — no aggregation enum, label, or doc implies non-sum targets exist; the dashboard card reduces toward "Chronicle entry + operations applied" per the operation-taxonomy direction; a compiler-level comment states the sum-only rule and the time_mean carve-out so the next reader doesn't re-invent the taxonomy.

Related meeting rulings recorded for coordination: geography is a plain constraint (thin presentation layers only), and the Chronicle-fact → target operation taxonomy (aging, entity conversion, subsetting) is the enumeration that makes targets code-free — María has partial issues on the UK epic; Anthony defining the lineage schema.

Start with packages/microcosm-build/src/microcosm/build/ledger_targets.py:22 and search above the compiler for count/mean branches, labels, enums, and documentation, including the calibration dashboard target card and Chronicle-to-target helpers. Check the related tests while tracing each occurrence. Done means only sum targets remain, the time_mean carve-out is documented at compiler level, and the dashboard wording follows the stated operation-taxonomy direction.