fix: address comprehensive code review findings

[nordicnode]

fix: address comprehensive code review findings

Harden verify output purity, fix render/diff edge cases, and clean up
repo hygiene:

• verify --verbose now routes the introspection block to stderr for every
  non-human format (github/junit included), keeping machine-readable stdout
  parseable
• add Trae to the --help ecosystem list and correct the README target count
  (18 -> 19)
• gitignore and remove committed agent-benchmark result artifacts (they
  contained machine-specific absolute paths), delete a stray = dir, and
  extend the CI package-content guard to block both
• dedupe ensure_no_symlink_ancestors into generate.rs, shared by
  init/update/--fix so the symlink-escape hardening can't drift
• time-box the verify_stdin write in spawn.rs (a child that never reads
  stdin can no longer hang the probe past HELP_TIMEOUT); regression test
• diff reports trailing-newline-only drift instead of "(no lines differ)"
• verify --fix suggestions point at skillpack.toml for config-driven checks
  (when_to_use/allowed_tools/plugin fields) so users don't loop on a no-op
• escape tabs in YAML descriptions and quotes/backslashes in glob lists;
  --target list honors --format json; strict is_json(); widen the watch
  noise filter; fix the misleading Shell/Powershell detection comment