feat(entity-store/b5): EdgeKeyKind::TextPair + archive verb — unblock kei-sage + kei-chat-store migration
schema.rs: EdgeKeyKind enum (IntegerPair default, TextPair) + archived_field:
Option<&'static str> on EntitySchema. Backward-compat via Default impl.
engine.rs: ddl_edge_table_for() dispatches integer vs text edge DDL.
Existing ddl_edge_table() untouched; new ddl_edge_table_text() adds
src_path/dst_path TEXT columns.
verbs/link.rs (rewrite): dispatches on edge_key_kind. Input JSON
{from:int, to:int} for IntegerPair OR {from:str, to:str} for TextPair.
verbs/rank.rs (rewrite): generic pagerank<K: Hash + Eq + Clone> over
node key type. Same algorithm, polymorphic in key.
verbs/archive.rs (new, 64 LOC): soft-delete via UPDATE <tbl> SET
<archived_field>=1 + optional <archived_field>_at=now(). Schema
without archived_field declared returns VerbError.
Tests: 20/20 kei-entity-store (was 10, +10: 5 text_pair + 5 archive).
kei-task 9/9 preserved (IntegerPair still default, backward-compat
verified).
Enables: kei-sage migration (TextPair edges) + kei-chat-store
migration (archive).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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