feat(skills): save-session skill for Claude Code

Records session facts (git log, diff --stat, deploys from transcript)
by appending to docs/sessions/YYYY-MM-DD.md with a mandatory narrative
placeholder. Never touches backlog.md or CLAUDE.md without explicit
instruction. Commits only the session file.

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

.claude/skills/save-session/SKILL.md

@@ -0,0 +1,65 @@
+---
+name: save-session
+description: Save and record the current work session to docs/sessions/. Trigger ONLY on explicit "save session", "zapisz sesję", or "wrap up" — never invoke proactively between tasks.
+---
+
+**Trigger condition**: user explicitly says "save session", "zapisz sesję", "wrap up", or equivalent.
+Never invoke proactively. Never invoke mid-task.
+
+## 1. Determine Session Boundary
+
+1. Read the latest entry file in `docs/sessions/` — use its last `## Session HH:MM` heading timestamp as the start boundary.
+2. Fallback if no previous entry exists: 24 hours ago.
+
+## 2. Collect Facts (deterministic only — no invention)
+
+Run exactly:
+```bash
+# All commits since boundary
+git --no-pager log --oneline <boundary>..HEAD
+
+# Changed file summary
+git --no-pager diff --stat <boundary>..HEAD
+```
+
+From the visible conversation transcript: deploys run and their outcomes, test results seen.
+
+## 3. Write the Session Entry
+
+**APPEND** to `docs/sessions/YYYY-MM-DD.md` (create the file if it doesn't exist for today).
+Never overwrite existing content.
+
+```markdown
+## Session HH:MM
+
+### Commits
+<output of git log --oneline>
+
+### Files changed
+<output of git diff --stat>
+
+### Deploys
+<list from transcript, or "None recorded">
+
+### Narrative
+> _user-provided summary_
+```
+
+The `> _user-provided summary_` placeholder is **mandatory**. Never fill it in. The user supplies the narrative separately if desired.
+
+## 4. What NOT to Touch
+
+- `backlog.md` — only on explicit "update backlog" instruction
+- `CLAUDE.md` — only on explicit "update CLAUDE.md" instruction
+- Any other file not listed above
+
+## 5. Commit
+
+Stage and commit **only** the session file:
+
+```bash
+git add docs/sessions/YYYY-MM-DD.md
+git commit -m "docs: session YYYY-MM-DD HH:MM"
+```
+
+No other files. No `git add -A`.