ci: make public-hygiene-lint green

[MattJackson]

public-hygiene-lint was RED on main in this repo. Every hit is fixed by rewriting the text to
state the BEHAVIOUR rather than our internal process. No allow markers were added anywhere in
this change: a blanket allow would turn the gate into decoration.

Hits found on main, and the decision for each

• .github/scripts/next-version.sh + .github/workflows/release-selftest.yml [internal-issue-id]
  cited an internal guard id. REWRITTEN: the sentences already state what the self-test does, so
  the id is simply dropped.
• tests/e2e.rs, tests/full_stack_e2e.rs [mutation-testing] named an internal QA harness as the
  example of a build invocation that does not uplift the cdylib. REWRITTEN to describe the build
  shape itself (a plain cargo test with no prior --all-targets/--lib build), which is the
  fact the helper actually depends on.

Red before green

Same invocation CI uses. Output is ASCII-folded for this description; the runs are verbatim
otherwise.

Before (on main)

$ python3 busbarAI/scripts/public-hygiene-lint.py --root .
== public-hygiene: what a customer reads, in . ==
  scanned 16 file(s) via git ls-files; 11 rules applied

  [internal-issue-id] internal issue / task / audit-round identifier - 2 hit(s)
      why: cites a tracker or audit artifact the reader cannot open; `task #141` and `R27 #8` shipped inside operator-facing API documentation
      .github/scripts/next-version.sh:5: # release automation can't silently rot (guard #135.8). Prints "v<MAJOR>.<MINOR>.<PATCH>" to stdout.
      .github/workflows/release-selftest.yml:1: # CI self-test for the release-on-upstream version-compute logic (guard #135.8).

  [mutation-testing] mutation-testing workflow leaked into shipped prose - 3 hit(s)
      why: names an internal QA tool and the campaign it was run in; the shipped comment should state the invariant the test protects, not the harness that found the gap
      tests/e2e.rs:113: /// (exactly what `cargo mutants`'s default build step runs, and what a developer running `cargo
      tests/e2e.rs:118: /// `cargo test` invocation `cargo-mutants` uses left `profile_dir` empty while `profile_dir/deps`
      tests/full_stack_e2e.rs:107: /// doc comment for the full story: a bare `cargo test` (what `cargo-mutants` runs, and what a

== result ==
  16 public file(s) scanned against 11 rules - 5 hit(s), 0 allowed
  public-hygiene-lint FAILED
  These lines describe how the software was BUILT, not what it does, in files a
  customer can read. Rewrite the text to state the behaviour or the invariant; if a
  line is genuinely legitimate, mark it:
    # public-hygiene-lint: allow - <why this text belongs in a public file>

After (this branch)

$ python3 busbarAI/scripts/public-hygiene-lint.py --root .
== public-hygiene: what a customer reads, in . ==
  scanned 16 file(s) via git ls-files; 11 rules applied

== result ==
  16 public file(s) scanned against 11 rules - 0 hit(s), 0 allowed
  public-hygiene-lint passed