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.

src/polygateway/telemetry/schema.py

@@ -155,6 +155,13 @@ def insert_sql(backend: str, columns: Sequence[str]) -> str:
     字符串拼进 SQL(占位符只保护值,保护不了列名)。sqlite 用 `?`、postgres 用 `$n`,
     两端的重复键处理都不绑定具体约束名(`INSERT OR IGNORE` / `ON CONFLICT`)。
 
+    **PG 的 `ON CONFLICT` 一律不带冲突目标,不得"顺手"补回 `(call_id)`**: PG 要求
+    分区表的唯一约束必须包含分区键,按 `created_at` 分区(issue #12 的保留期方案)后
+    主键变成 `(call_id, created_at)`,带目标的语句匹配不到任何约束,PG 直接拒收
+    ("there is no unique or exclusion constraint matching the ON CONFLICT
+    specification"),而遥测写失败只逐行 warning——分区部署下会全线静默丢数据。
+    无目标版本在两种表形态上都合法,普通表上语义逐字等价(表上只有主键一个唯一约束)。
+
     Args:
         backend: `"sqlite"` 或 `"postgres"`。
         columns: 要写入的列,顺序即占位符顺序(调用方须按同序取值)。
@@ -176,7 +183,7 @@ def insert_sql(backend: str, columns: Sequence[str]) -> str:
         placeholders = ", ".join("?" for _ in selected)
         return f"INSERT OR IGNORE INTO {TABLE} ({names}) VALUES ({placeholders})"
     placeholders = ", ".join(f"${i + 1}" for i in range(len(selected)))
-    return f"INSERT INTO {TABLE} ({names}) VALUES ({placeholders}) ON CONFLICT (call_id) DO NOTHING"
+    return f"INSERT INTO {TABLE} ({names}) VALUES ({placeholders}) ON CONFLICT DO NOTHING"
 
 
 def telemetry_schema_sql(backend: str) -> str: