Convert serve help test to fabro_snapshot and delete orphaned snap file

Replace ad-hoc insta::assert_snapshot! with TestContext + fabro_snapshot!
for consistency. Delete the orphaned snapshot file from the deleted
cli.rs module.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/crates/fabro-cli/tests/it/cmd/serve.rs

@@ -1,11 +1,10 @@
 #[test]
 #[cfg(feature = "server")]
 fn help() {
-    #[allow(deprecated)]
-    let mut cmd = assert_cmd::Command::cargo_bin("fabro").unwrap();
-    cmd.arg("--no-upgrade-check");
-    let output = cmd.args(["serve", "--help"]).output().expect("runs");
-    assert!(output.status.success());
-    let stdout = String::from_utf8(output.stdout).unwrap();
-    insta::assert_snapshot!(stdout);
+    use fabro_test::{fabro_snapshot, test_context};
+
+    let context = test_context!();
+    let mut cmd = context.command();
+    cmd.args(["serve", "--help"]);
+    fabro_snapshot!(context.filters(), cmd, @"");
 }

lib/crates/fabro-cli/tests/it/snapshots/it__cli__serve_help.snap

@@ -1,40 +0,0 @@
----
-source: lib/crates/fabro-cli/tests/it/cli.rs
-assertion_line: 747
-expression: stdout
----
-Start the HTTP API server
-
-Usage: fabro serve [OPTIONS]
-
-Options:
-      --debug
-          Enable DEBUG-level logging (default is INFO) [env: FABRO_DEBUG=]
-      --port <PORT>
-          Port to listen on [default: 3000]
-      --host <HOST>
-          Host address to bind to [default: 127.0.0.1]
-      --no-upgrade-check
-          Disable automatic upgrade check [env: FABRO_NO_UPGRADE_CHECK=]
-      --model <MODEL>
-          Override default LLM model
-      --quiet
-          Suppress non-essential output [env: FABRO_QUIET=]
-      --provider <PROVIDER>
-          Override default LLM provider
-      --verbose
-          Enable verbose output [env: FABRO_VERBOSE=]
-      --dry-run
-          Execute with simulated LLM backend
-      --storage-dir <STORAGE_DIR>
-          Storage directory (default: ~/.fabro) [env: FABRO_STORAGE_DIR=]
-      --sandbox <SANDBOX>
-          Sandbox for agent tools
-      --server-url <SERVER_URL>
-          Server URL (overrides server.base_url from user.toml) [env: FABRO_SERVER_URL=]
-      --max-concurrent-runs <MAX_CONCURRENT_RUNS>
-          Maximum number of concurrent run executions
-      --config <CONFIG>
-          Path to server config file (default: ~/.fabro/server.toml)
-  -h, --help
-          Print help