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/timefmt.rs

@@ -1,7 +1,7 @@
-//! Minimal UTC timestamp/duration formatting - no `chrono`/`time` dependency,
-//! matching vmic's minimal-dependency footprint. Timestamps are stored as
-//! Unix seconds (`i64`) everywhere in profile/instance state; this module
-//! only turns them into text for `status`/`list` output.
+//! Minimal UTC timestamp/duration formatting, without a `chrono`/`time`
+//! dependency. Timestamps are stored as Unix seconds (`i64`) everywhere in
+//! profile/instance state; this module only turns them into text for
+//! `status`/`list` output.
 
 use std::time::{SystemTime, UNIX_EPOCH};