fix(aggregator): body amount fallback — standalone total, paid labels win (#3121) - #3164

Fixes #3121 (Codex P2 from PR #2149, comment 4409381673, merged undispositioned).

The Gmail body-amount fallback regex had total as an unbounded alternative, so it matched the "total" inside "Subtotal": a body Subtotal $20.00 / Tax $1.60 / Total $21.60 recorded $20.00, and since exec() takes the first match, a later Amount paid $21.60 never won. The wrong amount also defeats cross-source dedupe.

Change (pm-stack/aggregator/scripts/produce-charge-candidates.ts):

• Extraction moved to an exported amountFromBody(): explicit paid/charged labels (amount paid | amount charged | total charged | transaction amount) win first; a standalone \btotal label is next (word boundary — "Subtotal" cannot match); any $ amount remains the last-resort fallback, as before.
• main() is now behind import.meta.main so the script is importable by tests without running the producer.

Tests (test/produce-charge-candidates.test.ts, new): Subtotal/Tax/Total + later Amount paid records 21.60; later Amount paid beats an earlier bare Total; standalone Total used when no paid label exists; total charged counts as paid/charged; no-amount body yields undefined. 5/5 pass on the laptop. Full aggregator suite: 712 pass / 7 fail — the 7 (page-manifest/nav renders) fail identically on clean origin/main in the same environment (verified via stash), pre-existing and unrelated.

Queue task 4554.

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