[pipelines] Core step library — map / filter / dedupe·upsert / paginate / reachability / geocode

[serge-ivo]

Child of #94.

Declarative pipelines (#94) compose reusable steps. Ship a first-party step catalog (each a registry tool, #85/#87) so the common data-shaping ops are config, not code:

• map/transform — rename/derive fields, extract nested (e.g. addressComponents → {city,suburb,state,country}), format.
• filter — keep/drop by predicate over fields.
• dedupe / upsert — by key field; skip-if-seen or update-in-place (respects collection unique constraints, MCP: instance-scoped collection read/write (insert_record/query_records/list_collections) #91).
• paginate / fan-out — iterate a source over pages or a generated set (e.g. grid cells around a centre), with a concurrency cap.
• http_reachable — GET a URL (browser UA, timeout, retry) → {ok, code}; the "is this site alive" probe.
• geocode — city/address → {lat,lng,country,state,locality} (via the generic HTTP connector + a maps provider).

Acceptance

• The lead-finder's transform/filter/dedupe/reachability/geocode steps are all expressible from this catalog — no custom code.