fix: drop the conflict target so partitioned tables can accept writes

PG requires a partitioned table's unique constraints to include the
partition key, so issue #12's RANGE partitioning on created_at forces
the primary key to (call_id, created_at). The old
`ON CONFLICT (call_id) DO NOTHING` then matches no constraint and PG
rejects every row with

    there is no unique or exclusion constraint matching the
    ON CONFLICT specification

which the recorder swallows as a per-row warning: telemetry would go
silently dark under a partitioned deployment. The target-free form is
valid on both table shapes and is literally equivalent on a plain table
(the primary key is its only unique constraint). SQLite's
`INSERT OR IGNORE` already carries no target and is untouched.

Integration coverage on the real PG instance, both inside self-created
temp schemas: a plain table still keeps one row per call_id, and a
table partitioned by created_at now accepts writes and reads them back.
The second case was red before this change with the error above.

tests/unit/test_telemetry.py

@@ -131,7 +131,9 @@ _FROZEN_PG_INSERT = (
     "sampling, reasoning_tokens, tenant_id, meta) "
     "VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, "
     "$19, $20, $21, $22, $23, $24) "
-    "ON CONFLICT (call_id) DO NOTHING"
+    # 无冲突目标(issue #13 Task 2): 带 `(call_id)` 的版本在按 created_at 分区、
+    # 主键为 (call_id, created_at) 的表上匹配不到约束,PG 直接拒收整条写入
+    "ON CONFLICT DO NOTHING"
 )
 
 
@@ -174,16 +176,17 @@ class TestSchemaModule:
         assert all("IF NOT EXISTS" not in stmt for _, stmt in PG_BACKFILL)
 
     def test_insert_sql_reproduces_the_frozen_statements(self):
-        """`insert_sql(backend, COLUMNS)` 必须与搬迁前的 `_INSERT` 逐字节相同。"""
+        """`insert_sql(backend, COLUMNS)` 与搬迁前的 `_INSERT` 一致(PG 侧去掉冲突目标)。"""
         from polygateway.telemetry.schema import COLUMNS, insert_sql
 
         assert insert_sql("sqlite", COLUMNS) == _FROZEN_SQLITE_INSERT
         assert insert_sql("postgres", COLUMNS) == _FROZEN_PG_INSERT
         # 裁剪列表按位置占位符重新编号,不留空洞
         assert insert_sql("postgres", ["call_id", "model"]) == (
-            "INSERT INTO llm_calls (call_id, model) VALUES ($1, $2) "
-            "ON CONFLICT (call_id) DO NOTHING"
+            "INSERT INTO llm_calls (call_id, model) VALUES ($1, $2) ON CONFLICT DO NOTHING"
         )
+        # 冲突目标不得被"顺手"补回: 分区表上它会让每一条遥测都被 PG 拒收
+        assert "ON CONFLICT (" not in insert_sql("postgres", COLUMNS)
 
     def test_insert_sql_rejects_foreign_columns_and_backends(self):
         """列名来自数据库探测结果而非常量,子集校验是唯一的注入面闸门。"""