feat: switch from tmux to simple nohup for remote jobs

- Remove tmux-based execution; jobs now run via nohup + shell script
- Remove p-agent daemon from workspace
- Remove `p attach` command (use `p logs -f` instead)
- Add `-d/--detach` flag to start job without streaming
- Stream output via SSH tail -F
- Ctrl+C detaches from stream; job keeps running
- `p stop` kills via PID file
- Worker requirements reduced to just rsync (no tmux needed)

Cargo.lock

@@ -73,12 +73,6 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
-[[package]]
-name = "base64"
-version = "0.22.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
-
 [[package]]
 name = "bitflags"
 version = "2.11.1"
@@ -476,7 +470,6 @@ name = "p"
 version = "0.1.0"
 dependencies = [
  "anyhow",
- "base64",
  "chrono",
  "clap",
  "ctrlc",
@@ -484,16 +477,10 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_yaml",
+ "shell-words",
  "uuid",
 ]
 
-[[package]]
-name = "p-agent"
-version = "0.1.0"
-dependencies = [
- "anyhow",
-]
-
 [[package]]
 name = "pin-project-lite"
 version = "0.2.17"
@@ -619,6 +606,12 @@ dependencies = [
  "unsafe-libyaml",
 ]
 
+[[package]]
+name = "shell-words"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc6fe69c597f9c37bfeeeeeb33da3530379845f10be461a66d16d03eca2ded77"
+
 [[package]]
 name = "shlex"
 version = "1.3.0"