feat: 后台服务模式 + 日志滚动 + 修复 llm_usage 表兼容性

- 新增 logger.rs（tracing-appender，日滚日志，.data/logs/）
- service 子命令：等同 listen --llm 但日志同时写入文件
- systemd/ias.service 单元文件
- 迁移 0007：ALTER TABLE llm_usage ADD COLUMN IF NOT EXISTS
  修复与 iPet 旧表的结构冲突
- ias usage 命令可正常查询 Token 统计
- 日志滚动保留 7 天，自动删除旧文件

Cargo.lock

@@ -467,6 +467,15 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82b8f8f868b36967f9606790d1903570de9ceaf870a7bf9fbbd3016d636a2cb2"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.6"
@@ -528,6 +537,15 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "deranged"
+version = "0.5.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7cd812cc2bc1d69d4764bd80df88b4317eaef9e773c75226407d9bc0876b211c"
+dependencies = [
+ "powerfmt",
+]
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -1127,6 +1145,7 @@ dependencies = [
  "sqlx",
  "tokio",
  "tracing",
+ "tracing-appender",
  "tracing-subscriber",
  "uuid",
 ]
@@ -1652,6 +1671,12 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "num-conv"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "521739c6d2bac4aa25192232afe6841231376b2b26d4d9fae5ecf8ca5772e441"
+
 [[package]]
 name = "num-derive"
 version = "0.4.2"
@@ -1876,6 +1901,12 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "powerfmt"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "439ee305def115ba05938db6eb1644ff94165c5ab5e9420d1c1bcedbba909391"
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.21"
@@ -2752,6 +2783,12 @@ version = "2.6.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "13c2bddecc57b384dee18652358fb23172facb8a2c51ccc10d74c157bdea3292"
 
+[[package]]
+name = "symlink"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7973cce6668464ea31f176d85b13c7ab3bba2cb3b77a2ed26abd7801688010a"
+
 [[package]]
 name = "syn"
 version = "2.0.117"
@@ -2860,6 +2897,37 @@ dependencies = [
  "zune-jpeg",
 ]
 
+[[package]]
+name = "time"
+version = "0.3.47"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "743bd48c283afc0388f9b8827b976905fb217ad9e647fae3a379a9283c4def2c"
+dependencies = [
+ "deranged",
+ "itoa",
+ "num-conv",
+ "powerfmt",
+ "serde_core",
+ "time-core",
+ "time-macros",
+]
+
+[[package]]
+name = "time-core"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7694e1cfe791f8d31026952abf09c69ca6f6fa4e1a1229e18988f06a04a12dca"
+
+[[package]]
+name = "time-macros"
+version = "0.2.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e70e4c5a0e0a8a4823ad65dfe1a6930e4f4d756dcd9dd7939022b5e8c501215"
+dependencies = [
+ "num-conv",
+ "time-core",
+]
+
 [[package]]
 name = "tinystr"
 version = "0.8.3"
@@ -3014,6 +3082,19 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-appender"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "050686193eb999b4bb3bc2acfa891a13da00f79734704c4b8b4ef1a10b368a3c"
+dependencies = [
+ "crossbeam-channel",
+ "symlink",
+ "thiserror",
+ "time",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "tracing-attributes"
 version = "0.1.31"