Fix CRLF distribution for .bat files; add DLL-specific caveat hint - #435

* Fix two stale post-#435 messages; close Item 51; file Item 59

A high-confidence external review (working from the repo alone, no CI
log access) caught two places the CRLF distribution fix (#435) landed
but didn't revisit:

- run_setup.bat's own line-ending self-check panel still told a
  confused user to "re-download using git clone, not the Raw button" --
  true before #435, false and actively bad advice after it (steers a
  git-less Prime Directive user toward a tool they don't have, instead
  of just re-downloading via the now-fixed Raw link). The panel and its
  header comment now describe the check as defense-in-depth against a
  stale/re-saved copy, not a workaround for a still-broken channel.
- :merge_git_config (REQ-015) still wrote *.bat eol=crlf / *.cmd
  eol=crlf into every bootstrapped user's OWN .gitattributes -- the
  exact pattern this repo just proved insufficient for itself. Changed
  to *.bat -text / *.cmd -text, matching this repo's own .gitattributes.

Both fixes updated their matching test assertions
(selfapps_lineending_check.ps1, selfapps_ux_hardening.ps1) and the
REQ-015 spec in README.md in lockstep.

Also closes Active Backlog Item 51 (HP_PIPREQS_RC errorlevel-capture
ordering): the same review settled the underlying cmd.exe semantics
question (a successful plain "set" does not itself touch %errorlevel%,
so this was very likely never a live bug) but the zero-risk reorder fix
was applied anyway, exactly as the item's own note recommended, closing
the cross-call-site inconsistency regardless of who's right.

Files Active Backlog Item 59: CodeRabbit's automated review did not run
on PR #435 (manual-trigger-required repo config) -- standing directive
for future PRs to trigger it via @coderabbitai review, plus a record of
what this pass caught as the motivating evidence.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017SQ1rvJxDbE71pTXJ4QvLV

* Fix CodeRabbit findings on PR #436

Two real issues caught by CodeRabbit's review:

- selfapps_ux_hardening.ps1's whole-script $allPass aggregate (line
  1184) still referenced $gaBatCrlf, the variable renamed to
  $gaBatText earlier in this same PR. Under PowerShell's non-strict
  mode the undefined reference silently evaluated to $null, making
  $allPass always false regardless of actual test outcomes -- this
  script would have always exited 1. Fixed to reference $gaBatText.

- selfapps_ux_hardening.ps1's non-Windows skip guard used $IsWindows,
  which is undefined under Windows PowerShell 5.1 (only introduced in
  PowerShell 6+). The identical bug was already fixed in the sibling
  selfapps_lineending_check.ps1 (PR #434); this file had not been
  updated to match. Fixed to the same
  [System.Environment]::OSVersion.Platform pattern.

A third finding (:merge_git_config doesn't migrate an existing
.gitattributes with the old eol=crlf rules to -text) is real and
correctly rated "Major, Heavy lift" by CodeRabbit -- left for a
follow-up rather than folded into this PR; it needs a real
read-modify-write against a user's own file plus a new regression
scenario, not a quick fix.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017SQ1rvJxDbE71pTXJ4QvLV

* File Item 60: REQ-015 does not migrate an existing .gitattributes

CodeRabbit's review on PR #436 (rated Major, Heavy lift) correctly
identified that the idempotency guard in :merge_git_config means a
user who already ran an older run_setup.bat keeps *.bat eol=crlf /
*.cmd eol=crlf forever -- item 59's fix only covers a fresh append,
not migrating existing content. Real design questions (replace vs.
append-superseding-rules) mean this needs its own scoping pass rather
than a rushed fix folded into this PR.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017SQ1rvJxDbE71pTXJ4QvLV

* Fix two more CodeRabbit findings on PR #436

- Test 4's .gitattributes assertion only checked *.bat -text, never
  *.cmd -text, even though :merge_git_config writes both. A regression
  in the .cmd rule specifically could have passed silently. Added
  $gaCmdText, included in both the row's own pass condition and the
  whole-script $allPass aggregate.
- Tagged the -text rationale comment as "# derived requirement:" per
  this repo's own convention for non-obvious constraints.

Verified: PS AST parse clean, check_delimiters.py clean (one
pre-existing, unrelated finding at a shifted line number, confirmed
present before this change too), ASCII clean, markdownlint-cli2
CLAUDE.md clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017SQ1rvJxDbE71pTXJ4QvLV

---------

Co-authored-by: Claude <noreply@anthropic.com>