fix: /retro bare dates use wall-clock time, not midnight (v0.8.5) (#211)

* fix: /retro bare dates use wall-clock time, not midnight

Git interprets --since="2026-03-11" as the current wall-clock time
on that date, not midnight. Append T00:00:00 to all date examples
so /retro always captures full calendar days.

* chore: bump version and changelog (v0.8.5)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- **`/retro` now counts full calendar days.** Running a retro late at night no longer silently misses commits from earlier in the day. Git treats bare dates like `--since="2026-03-11"` as "11pm on March 11" if you run it at 11pm — now we pass `--since="2026-03-11T00:00:00"` so it always starts from midnight. Compare mode windows get the same fix.
 - **Review log no longer breaks on branch names with `/`.** Branch names like `garrytan/design-system` caused review log writes to fail because Claude Code runs multi-line bash blocks as separate shell invocations, losing variables between commands. New `gstack-review-log` and `gstack-review-read` atomic helpers encapsulate the entire operation in a single command.
 - **All skill templates are now platform-agnostic.** Removed Rails-specific patterns (`bin/test-lane`, `RAILS_ENV`, `.includes()`, `rescue StandardError`, etc.) from `/ship`, `/review`, `/plan-ceo-review`, and `/plan-eng-review`. The review checklist now shows examples for Rails, Node, Python, and Django side-by-side.
 - **`/ship` reads CLAUDE.md to discover test commands** instead of hardcoding `bin/test-lane` and `npm run test`. If no test commands are found, it asks the user and persists the answer to CLAUDE.md.