Show real mapping grammar in --help, make --via repeatable, trim comments

- -l/-r/-d now show their actual grammar as the clap value name
  (<[BIND:]PORT:HOST:PORT>, <[BIND:]PORT>) instead of a generic <SPEC>,
  matching vmic's convention of showing real syntax in --help. The
  grammar is no longer also repeated in the flag's help text, since the
  value name already carries it.
- --via changes from a single comma-separated flag to a repeatable one
  (Vec<String> + value_delimiter = ','), so both `--via a --via b` and
  `--via a,b` work and can be mixed. commands/mod.rs's edits_from_mapping
  no longer needs to split the string itself - clap does it.
- Trimmed CLI help text that restated grammar/rationale already covered
  by the value name or by --via being required.
- Normalized code comments for tone/format consistency: dropped
  cross-references to vmic's own internals as justification (this
  codebase should read as self-contained), removed markdown-style
  *emphasis* asterisks that don't render in plain comments, tightened
  several run-on sentences into plain declarative ones, and fixed one
  comment in wipe.rs that inaccurately described close_instance's force
  path (it sends SIGKILL, not SIGTERM).
- spec/porthole-spec.md's --via row updated to document the repeatable
  form alongside comma-separated.

Cargo.toml/Cargo.lock/atomic.rs also carry an external toml crate bump
and formatting pass picked up from the working tree.

src/cli.rs

@@ -54,24 +54,23 @@ pub enum Commands {
 /// struct (`#[command(flatten)]`ed into both) so the two can never drift.
 #[derive(Args, Default)]
 pub struct MappingArgs {
-    /// Local forward: your machine -> remote. [bind:]port:host:hostport
-    #[arg(short, long, value_name = "SPEC")]
+    /// Local forward: your machine -> remote.
+    #[arg(short, long, value_name = "[BIND:]PORT:HOST:PORT")]
     pub local: Option<String>,
 
-    /// Remote forward: remote -> your machine. [bind:]port:host:hostport
-    #[arg(short, long, value_name = "SPEC")]
+    /// Remote forward: remote -> your machine.
+    #[arg(short, long, value_name = "[BIND:]PORT:HOST:PORT")]
     pub remote: Option<String>,
 
-    /// Dynamic forward (SOCKS proxy). [bind:]port
-    #[arg(short, long, value_name = "SPEC")]
+    /// Dynamic forward (SOCKS proxy).
+    #[arg(short, long, value_name = "[BIND:]PORT")]
     pub dynamic: Option<String>,
 
-    /// SSH hop chain, comma-separated: [user@]host[:port][,...]. The last
-    /// hop is the actual connection target, any before it are -J jumps.
-    #[arg(long, value_name = "HOPS")]
-    pub via: Option<String>,
+    /// SSH hop chain: jump hosts plus the final connection target.
+    #[arg(long, value_name = "[USER@]HOST[:PORT]", value_delimiter = ',')]
+    pub via: Vec<String>,
 
-    /// Default user for the target and any --via hop without its own.
+    /// Default user for the target and any hop without one.
     #[arg(short, long, value_name = "USER")]
     pub user: Option<String>,