feat(observability): Add metrics, logging, and sync-run core modules

Introduce the foundational observability layer for the sync pipeline:

- MetricsLayer: Custom tracing subscriber layer that captures span timing
  and structured fields, materializing them into a hierarchical
  Vec<StageTiming> tree for robot-mode performance data output
- logging: Dual-layer subscriber infrastructure with configurable stderr
  verbosity (-v/-vv/-vvv) and always-on JSON file logging with daily
  rotation and configurable retention (default 30 days)
- SyncRunRecorder: Compile-time enforced lifecycle recorder for sync_runs
  table (start -> succeed|fail), with correlation IDs and aggregate counts
- LoggingConfig: New config section for log_dir, retention_days, and
  file_logging toggle
- get_log_dir(): Path helper for log directory resolution
- is_permanent_api_error(): Distinguish retryable vs permanent API failures
  (only 404 is truly permanent; 403/auth errors may be environmental)

Database changes:
- Migration 013: Add resource_events_synced_for_updated_at watermark columns
  to issues and merge_requests tables for incremental resource event sync
- Migration 014: Enrich sync_runs with run_id correlation ID, aggregate
  counts (total_items_processed, total_errors), and run_id index
- Wrap file-based migrations in savepoints for rollback safety

Dependencies: Add uuid (run_id generation), tracing-appender (file logging)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.lock

@@ -296,6 +296,21 @@ 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-utils"
+version = "0.8.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
+
 [[package]]
 name = "crossterm"
 version = "0.29.0"
@@ -347,6 +362,15 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "092966b41edc516079bdf31ec78a2e0588d1d0c08f78b91d8307215928642b2b"
 
+[[package]]
+name = "deranged"
+version = "0.5.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ececcb659e7ba858fb4f10388c250a7252eb0a27373f1a72b8748afdd248e587"
+dependencies = [
+ "powerfmt",
+]
+
 [[package]]
 name = "dialoguer"
 version = "0.12.0"
@@ -1108,6 +1132,7 @@ dependencies = [
  "thiserror",
  "tokio",
  "tracing",
+ "tracing-appender",
  "tracing-subscriber",
  "url",
  "urlencoding",
@@ -1183,6 +1208,12 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "num-conv"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf97ec579c3c42f953ef76dbf8d55ac91fb219dde70e49aa4a6b7d74e9919050"
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -1343,6 +1374,12 @@ 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"
@@ -1878,6 +1915,37 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "time"
+version = "0.3.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9da98b7d9b7dad93488a84b8248efc35352b0b2657397d4167e7ad67e5d535e5"
+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 = "0.2.26"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78cc610bac2dcee56805c99642447d4c5dbde4d01f752ffea0199aee1f601dc4"
+dependencies = [
+ "num-conv",
+ "time-core",
+]
+
 [[package]]
 name = "tinystr"
 version = "0.8.2"
@@ -2003,6 +2071,18 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-appender"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "786d480bce6247ab75f005b14ae1624ad978d3029d9113f0a22fa1ac773faeaf"
+dependencies = [
+ "crossbeam-channel",
+ "thiserror",
+ "time",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "tracing-attributes"
 version = "0.1.31"
@@ -2035,6 +2115,16 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-serde"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "704b1aeb7be0d0a84fc9828cae51dab5970fee5088f83d1dd7ee6f6246fc6ff1"
+dependencies = [
+ "serde",
+ "tracing-core",
+]
+
 [[package]]
 name = "tracing-subscriber"
 version = "0.3.22"
@@ -2045,12 +2135,15 @@ dependencies = [
  "nu-ansi-term",
  "once_cell",
  "regex-automata",
+ "serde",
+ "serde_json",
  "sharded-slab",
  "smallvec",
  "thread_local",
  "tracing",
  "tracing-core",
  "tracing-log",
+ "tracing-serde",
 ]
 
 [[package]]