test(desktop): use a wordlist-safe separator in passphrase word-count test

[ngthuydiem]

Summary

Fixes #6249.

key_backup::tests::generated_passphrase_respects_word_count_and_separator joined words with - and asserted the phrase splits back into exactly count parts. The EFF short wordlist contains exactly one hyphenated entry (yo-yo, line 1281 of 1296), so drawing it into either hyphen-joined arm yields one extra part — a ~1-in-186 flake per full suite run (1 - (1 - 1/1296)^7 ≈ 0.539%).

This switches the two hyphen arms to |, which cannot appear in the wordlist — the exact guard the sibling test generated_passphrase_clamps_word_count already documents and uses. The space, dot, and empty-separator arms are untouched (no wordlist entry contains a space or a dot), so the test still covers word count, wordlist membership, and minimum length.

generate_passphrase itself is unchanged — a hyphenated word in a hyphen-joined passphrase is not a product defect, only an ambiguity the test's parsing could not handle.

Verification

At main (196d62f), compiled the desktop test binary once and looped it 2000× per state:

State	Failures / 2000 runs	Expected
old code	15	~10.8 (P ≈ 0.539%)
fixed	0	0

Full desktop Tauri suite (cargo test --workspace in desktop/src-tauri): 2693 passed, 0 failed.

[ngthuydiem]

The full EFF wordlist includes 4 words with "-" in them: https://www.eff.org/files/2016/07/18/eff_large_wordlist.txt

[ngthuydiem]

Loop to run this test n times given its flakiness:

RUST_BACKTRACE=1 cargo test --manifest-path desktop/src-tauri/Cargo.toml --lib --no-run
for i in $(seq 1000); do
    printf '\riteration %d' "$i"
    desktop/src-tauri/target/debug/deps/buzz_lib-ac080c7e34975d7e \
      key_backup::tests::generated_passphrase >/dev/null 2>&1 \
      || { echo " FAILED on iteration $i"; break; }
  done

[ngthuydiem]

Verification:

• Before on main:

• After on fix branch:

[wesbillman]

Carl, an automated reviewer, commenting via Wes’s GitHub account.

Reviewed exact head f2828d5c2ec1b58ed19dac1c4cadc001b1eb385f against base f96f1883c5ad94825d43a856e5d25e307a0540cb. No material findings.

The failure mechanism and repair match: the bundled 1,296-entry wordlist contains yo-yo, while it contains no pipe, space, or dot characters. Replacing the two hyphen-delimited cases with | therefore makes split-based word-count and membership assertions unambiguous without changing production passphrase generation. The sibling clamp test already uses the same invariant, and the remaining cases still exercise alternate and empty separators.

Validation: exact-head wordlist invariants and git diff --check passed; all applicable GitHub checks on this head are complete and green. I did not rerun CI-equivalent suites locally. I am leaving a comment rather than approving because Wes requested review, not approval.