[chore] add claude skill to sync upstream into sigma fork

.claude/commands/sync-upstream.md

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+# Sync Upstream into Sigma Fork
+
+Sync the sigmacomputing fork of sqlparser-rs with commits from the apache upstream remote.
+
+## Instructions
+
+### Step 1: Determine the sync target
+
+The user may have provided a sync target as an argument: `$ARGUMENTS`
+
+If a target was provided, interpret it as one of:
+- `latest` or empty — sync to `upstream/main` HEAD
+- `latest-tag` — sync to the most recent upstream tag
+- A tag name like `v0.61.0` — sync to that specific tag
+- A commit hash — sync to that specific commit
+
+If no argument was provided, first fetch remotes and gather context, then ask the user:
+```bash
+git fetch origin
+git fetch upstream --tags
+
+# Gather info for the prompt:
+git log -1 --format="%h %s (%ci)" upstream/main          # latest commit
+git tag --list --sort=-version:refname | grep -E '^v?[0-9]' | head -1  # latest tag name
+git log -1 --format="%h %s (%ci)" $(git tag --list --sort=-version:refname | grep -E '^v?[0-9]' | head -1)  # latest tag commit info
+```
+
+Use AskUserQuestion with the gathered info included in each option description:
+1. **Latest commit on upstream/main** — show the commit hash, message, and date
+2. **Latest tag** — show the tag name, commit hash, and date
+3. **Specific tag** — prompt for tag name (list a few recent tags with dates as context)
+4. **Specific commit** — prompt for commit hash
+
+Once the target is known, resolve it:
+```bash
+# Latest commit:   TARGET=upstream/main
+# Latest tag:      TARGET=$(git tag --list --sort=-version:refname | grep -E '^v?[0-9]' | head -1)
+# Specific tag:    TARGET=<tag>
+# Specific commit: TARGET=<hash>
+
+git rev-parse $TARGET   # confirm it resolves
+```
+
+### Step 2: Create a new branch off the target
+
+Name the branch to reflect what's being synced:
+```bash
+git checkout -b ayman/sync-upstream-$(date +%Y%m%d) $TARGET
+```
+
+### Step 3: Merge origin/main
+```bash
+git merge origin/main --no-ff -m "Merge sigma origin/main into upstream/main for sync"
+```
+
+This will likely produce conflicts. Do NOT abort — proceed to resolve them.
+
+### Step 4: Resolve all merge conflicts
+
+For each conflicted file:
+
+1. **Understand sigma's intent**: Look at the original sigma commits and PRs to understand the purpose behind each change. Use `git log`, `git show`, and the GitHub PR history as needed.
+
+2. **Understand upstream's changes**: Determine whether upstream's changes cover, supersede, or are orthogonal to sigma's changes.
+
+3. **Default resolution**: Keep changes from BOTH sides unless one side clearly supersedes the other. Never discard either side without good reason.
+
+4. Ask the user if uncertain about any conflict resolution.
+
+After resolving all conflicts in all files:
+```bash
+git add <all-resolved-files>
+git commit --no-edit   # completes the merge commit
+```
+
+All conflict resolutions must be in the single merge commit.
+
+### Step 5: Fix compilation and test issues
+
+```bash
+cargo clippy --all-features --all-targets
+```
+
+Investigate and fix any errors or warnings. Commit fixes as a separate commit (do not amend the merge commit).
+
+### Step 6: Run full verification
+
+```bash
+cargo fmt
+cargo clippy --all-features --all-targets
+cargo test --all-features --all-targets
+```
+
+All must pass before creating the PR. Fix any remaining issues and commit them.
+
+### Step 7: Push and create PR
+
+```bash
+git push origin ayman/sync-upstream-$(date +%Y%m%d)
+gh pr create \
+  --repo sigmacomputing/sqlparser-rs \
+  --base main \
+  --head ayman/sync-upstream-$(date +%Y%m%d) \
+  --title "[chore] Sync upstream apache/datafusion-sqlparser-rs into sigma fork" \
+  --body "..."
+```
+
+The PR description must include:
+- The upstream ref being synced to (commit hash, tag, or HEAD) and what it corresponds to
+- Number of upstream commits brought in
+- Summary of notable upstream changes (new features, dialects, fixes)
+- List of all sigma features confirmed preserved
+- Summary of each conflict resolved and how
+- Checklist confirming clippy, fmt, and tests all pass

.claude/settings.json

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+{
+  "permissions": {
+    "allow": [
+      "Bash(git fetch:*)",
+      "Bash(git merge:*)",
+      "Bash(echo \"EXIT: $?\")",
+      "Bash(cargo build:*)",
+      "Bash(cargo test:*)",
+      "Bash(git add:*)",
+      "Bash(git push:*)",
+      "Bash(gh pr:*)",
+      "Bash(git stash:*)",
+      "Bash(git checkout:*)",
+      "Bash(gh auth:*)",
+      "Bash(git remote:*)",
+      "Bash(gh repo:*)",
+      "Bash(git log:*)",
+      "Bash(git commit:*)",
+      "Bash(cargo fmt:*)",
+      "Bash(cargo clippy:*)"
+    ]
+  }
+}