fix(allowlist): lower default auto-apply threshold 0.95 → 0.90

Operator evidence 2026-06-07: 0.95 was too strict, skipping confident-enough
auto-applications of accepted tags. Newly-accepted tags now allowlist at 0.90;
existing entries keep their stored value and per-tag thresholds stay tunable in
the allowlist table. No migration — min_confidence has no DB server_default, so
the Python insert default governs new rows only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/models/tag_allowlist.py

@@ -22,7 +22,11 @@ class TagAllowlist(Base):
     tag_id: Mapped[int] = mapped_column(
         ForeignKey("tag.id", ondelete="CASCADE"), primary_key=True
     )
-    min_confidence: Mapped[float] = mapped_column(Float, nullable=False, default=0.95)
+    # Default auto-apply threshold for a newly-accepted tag. 0.90 (lowered from
+    # 0.95 on operator evidence 2026-06-07: 0.95 was too strict and skipped
+    # confident-enough applications). Per-tag value is still tunable in the
+    # allowlist table; existing rows keep whatever they were stored with.
+    min_confidence: Mapped[float] = mapped_column(Float, nullable=False, default=0.90)
     added_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now()
     )