Add .frs_resolve_aoi() internal helper for network-agnostic AOI resolution

[NewGraphEnvironment]

Problem

Every new manipulation function (frs_break(), frs_classify(), frs_aggregate()) needs to resolve an AOI parameter into a SQL predicate. This logic is shared infrastructure.

Proposed Solution

Internal helper .frs_resolve_aoi() that normalizes any AOI input to a SQL predicate:

Input	Resolution
Character vector ("BULK", c("BULK", "MORR"))	WHERE {partition_col} IN (...)
sf polygon	ST_Intersects(geom, ...)
list(blk = ..., measure = ...)	Delineate watershed via fwa_watershedatmeasure(), then spatial predicate
NULL	No spatial filter

Network-agnostic design

The partition column is configurable via options(fresh.partition_col = "watershed_group_code"). Default is FWA's WSG code. A spyda-built network sets options(fresh.partition_col = "basin_id") or whatever its partition scheme uses. No FWA concepts baked into the resolver logic.

This aligns with the broader options() pattern for network flexibility:

options(
  fresh.partition_col = "watershed_group_code",  # FWA default
  fresh.stream_table = "whse_basemapping.fwa_stream_networks_sp",
  fresh.blk_col = "blue_line_key",
  fresh.measure_col = "downstream_route_measure"
)

Dependencies

Build this before frs_break(), frs_classify(), frs_aggregate() — they all consume it.