v0.4.2: bls_search_series headline series fix, concept/synonym resolution

bls_search_series headline series fix, concept/synonym resolution

bls_search_series now unions headline common series into the candidate
set before the relevance rescore (fixing #35 where CUUR0000SA0 was
dropped for 'CPI' queries), and adds concept/synonym resolution so
'inflation' → CU, 'jobs'/'payroll' → CE, 'PPI' → WP/PC, etc. (#36).
bls_get_series calculations wording corrected (#37).

Fixed:

• bls_search_series: headline common series (e.g. CUUR0000SA0) now
  always unioned into candidates, independent of FTS5 cap (#35)

Added:

• CONCEPT_ALIASES map resolves economic vocabulary to BLS survey codes;
  matching surveys get a relevance boost in the rescore (#36)

Changed:

• bls_get_series calculations description corrected: survey returns
  whichever calculations it supports; CPI/PPI return percent change
  only, with no error; only surveys supporting neither return an error (#37)

Internal:

• observations ingester/service: non-null assertions replaced with
  for...of entries(), bracket-key access replaced with dot notation

162 tests pass; bun run devcheck clean.