Unified pipeline: frs_network_segment + frs_habitat_classify

[NewGraphEnvironment]

Summary

Two new exported functions for the unified pipeline (#83):

• frs_network_segment() — domain-agnostic network segmentation. Extracts, enriches, breaks at any number of sources, assigns id_segment. One table, one copy of geometry, shared across species.

• frs_habitat_classify() — long-format habitat classification. One row per segment x species. Species-specific accessibility via break label filtering (gradient_15 blocks CO but not BT).

Also: .frs_sql_num() for locale-safe numeric SQL, auto-indexing on label, id_segment, species_code.

Output structure

fresh.streams         — 19,048 segments (geometry, once)
fresh.streams_habitat — 57,144 rows (3 species x segments, no geometry)
fresh.streams_breaks  — enriched breaks with ltree codes + labels

Species-specific accessibility

Species	Access threshold	Accessible segments
CO	15%	3,719
ST	20%	5,139
BT	25%	7,219

Test plan

• devtools::test() — 528 pass, 0 fail
• Code review — 2 rounds, locale fix applied
• End-to-end: barriers → segment → classify on ADMS
• Multi-threshold accessibility verified (CO < ST < BT)
• id_segment unique across all segments

Fixes #83
Relates to #82, #86
Relates to NewGraphEnvironment/sred-2025-2026#16

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