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/commands/mod.rs

@@ -11,12 +11,13 @@ pub mod wipe;
 use crate::cli::MappingArgs;
 use crate::profile::ProfileEdits;
 
-/// Turns clap's `MappingArgs` into a `ProfileEdits`, splitting `--via`'s
-/// comma-separated raw string into the ordered hop list (spec §5.1).
+/// Turns clap's `MappingArgs` into a `ProfileEdits` (spec §5.1). `--via` is
+/// collected by clap itself: `value_delimiter = ','` splits each
+/// occurrence on commas, and the field being a `Vec` allows repeated
+/// `--via` flags, so both `--via a,b` and `--via a --via b` reach here as
+/// `["a", "b"]`.
 pub fn edits_from_mapping(m: &MappingArgs) -> ProfileEdits {
-    let via = m.via.as_deref().map(|raw| {
-        raw.split(',').map(str::trim).filter(|s| !s.is_empty()).map(str::to_string).collect::<Vec<_>>()
-    });
+    let via = (!m.via.is_empty()).then(|| m.via.clone());
     ProfileEdits {
         local: m.local.clone(),
         remote: m.remote.clone(),
@@ -33,12 +34,12 @@ pub fn edits_from_mapping(m: &MappingArgs) -> ProfileEdits {
 }
 
 /// `true` if `MappingArgs` carries no edits at all - used by `edit` to
-/// reject a no-op invocation the same way vmic's commands do.
+/// reject a no-op invocation.
 pub fn mapping_is_empty(m: &MappingArgs) -> bool {
     m.local.is_none()
         && m.remote.is_none()
         && m.dynamic.is_none()
-        && m.via.is_none()
+        && m.via.is_empty()
         && m.user.is_none()
         && m.identity.is_none()
         && m.port.is_none()