Use installed dosh-auth path for SSH bootstrap

SPEC.md

@@ -3,7 +3,7 @@
 **Status:** Implemented Rust build with local and Docker SSH verification  
 **Default language:** Rust, unless benchmarks prove the stack is the bottleneck  
 **Binaries:** `dosh-server`, `dosh-client`, `dosh-auth`, `dosh-bench`  
-**Helper mode:** `dosh-server auth` or `dosh-auth`, invoked by SSH with `-T`
+**Helper mode:** `dosh-server auth` or `~/.local/bin/dosh-auth`, invoked by SSH with `-T`
 
 ---
 
@@ -96,7 +96,7 @@ host/user/session/mode:
    - Receives `AttachOk` with session key, `ClientId`, and snapshot.
 
 3. **SSH bootstrap**
-   - Runs `ssh -T user@host dosh-auth ...`.
+   - Runs `ssh -T user@host ~/.local/bin/dosh-auth ...`.
    - Receives attach token, attach ticket, session key material, and server metadata.
    - Sends `BootstrapAttachRequest`.
    - Receives `AttachOk` with `ClientId` and snapshot.
@@ -185,7 +185,7 @@ No terminal bytes are sent outside AEAD after the attach handshake begins.
 Client command:
 
 ```bash
-ssh -T user@host dosh-auth \
+ssh -T user@host ~/.local/bin/dosh-auth \
   --protocol 1 \
   --nonce <client_nonce> \
   --session <name> \
@@ -454,6 +454,7 @@ Client config: `~/.config/dosh/client.toml`
 
 ```toml
 server = "user@example.com"
+ssh_auth_command = "~/.local/bin/dosh-auth"
 # ssh_port = 22
 dosh_port = 50000
 default_session = "default"