feat: GitLab support for /retro, /ship, and /document-release (v0.11.20.0) (#508)

* feat: multi-platform BASE_BRANCH_DETECT (GitHub + GitLab + GHE + git-native)

Update the shared BASE_BRANCH_DETECT resolver to support GitHub, GitLab,
GitHub Enterprise, self-hosted GitLab, and a git-native fallback chain.
Platform detection uses remote URL matching plus CLI auth status for
custom domains. Add glab issue create alternative in test failure triage.

Add 7 new test assertions covering GitLab CLI presence, git symbolic-ref
fallback, and platform-specific output in retro and ship generated files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: GitLab support in /retro — use shared BASE_BRANCH_DETECT resolver

Replace retro's custom gh-only default branch detection with the shared
BASE_BRANCH_DETECT resolver (DRY — same as 10 other skills). Update
PR/MR number extraction to match both GitHub #NNN and GitLab !NNN
patterns. Remove hardcoded github.com URL from the personal card footer.
Regenerate all SKILL.md files affected by the resolver update.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: GitLab MR creation in /ship + /document-release

Ship Step 1.5 now checks .gitlab-ci.yml for release workflows alongside
GitHub Actions. Step 8 routes to glab mr create on GitLab repos with
correct flag mapping (-b, -t, -d). Falls back to manual instructions
when no CLI is available. Document-release now reads MR body via
glab mr view -F json and updates via glab mr update on GitLab repos.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: add P2 TODO for land-and-deploy GitLab support

Track the remaining work to support GitLab in /land-and-deploy — MR
merge, CI polling, and deploy workflow detection using glab equivalents.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: adversarial review — GitLab gate, shell safety, MR prefix preservation

Three fixes from adversarial review:
1. land-and-deploy: add GitLab gate after Step 0 — prevents detection/
   execution mismatch where agent detects GitLab but all subsequent
   steps are GitHub-only
2. document-release: use heredoc for glab mr update body to avoid shell
   metacharacter mangling ($, backticks, !) in MR descriptions
3. retro: preserve original #/! prefix in PR/MR number extraction —
   GitLab !42 stays as !42, not incorrectly converted to #42

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: resolve merge conflicts — deduplicate gen-skill-docs resolvers

The merge from main created duplicate RESOLVERS records in gen-skill-docs.ts
(inline functions shadowing the imported module versions). Removed the inline
duplicates so the modular resolvers from scripts/resolvers/ are used.
Also added missing E2E_TIERS entries for plan-completion/verification tests.

* chore: bump version and changelog (v0.11.20.0)

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

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

document-release/SKILL.md.tmpl

@@ -291,14 +291,20 @@ EOF
 git push
 ```
 
-**PR body update (idempotent, race-safe):**
+**PR/MR body update (idempotent, race-safe):**
 
-1. Read the existing PR body into a PID-unique tempfile:
+1. Read the existing PR/MR body into a PID-unique tempfile (use the platform detected in Step 0):
 
+**If GitHub:**
 ```bash
 gh pr view --json body -q .body > /tmp/gstack-pr-body-$$.md
 ```
 
+**If GitLab:**
+```bash
+glab mr view -F json 2>/dev/null | python3 -c "import sys,json; print(json.load(sys.stdin).get('description',''))" > /tmp/gstack-pr-body-$$.md
+```
+
 2. If the tempfile already contains a `## Documentation` section, replace that section with the
    updated content. If it does not contain one, append a `## Documentation` section at the end.
 
@@ -308,18 +314,28 @@ gh pr view --json body -q .body > /tmp/gstack-pr-body-$$.md
 
 4. Write the updated body back:
 
+**If GitHub:**
 ```bash
 gh pr edit --body-file /tmp/gstack-pr-body-$$.md
 ```
 
+**If GitLab:**
+Read the contents of `/tmp/gstack-pr-body-$$.md` using the Read tool, then pass it to `glab mr update` using a heredoc to avoid shell metacharacter issues:
+```bash
+glab mr update -d "$(cat <<'MRBODY'
+<paste the file contents here>
+MRBODY
+)"
+```
+
 5. Clean up the tempfile:
 
 ```bash
 rm -f /tmp/gstack-pr-body-$$.md
 ```
 
-6. If `gh pr view` fails (no PR exists): skip with message "No PR found — skipping body update."
-7. If `gh pr edit` fails: warn "Could not update PR body — documentation changes are in the
+6. If `gh pr view` / `glab mr view` fails (no PR/MR exists): skip with message "No PR/MR found — skipping body update."
+7. If `gh pr edit` / `glab mr update` fails: warn "Could not update PR/MR body — documentation changes are in the
    commit." and continue.
 
 **Structured doc health summary (final output):**