ci: add gemini-manual workflow and headless agent skills (#52)

### Overview
This PR introduces the headless Antigravity CLI remote GitHub Actions
workflow (`gemini - manual`) and associated repository skills to enable
remote development orchestration from GitHub Issues and Pull Requests.

### Key Changes
1. **GitHub Actions Workflow (`.github/workflows/gemini-manual.yml`)**:
   - Collaborator access guard (`OWNER`, `MEMBER`, `COLLABORATOR`).
   - Interactive emoji reactions (`eyes` and `rocket`).
- Multi-turn conversation persistence via `actions/cache@v4` on
`~/.gemini/antigravity-cli/conversations` and `brain/`.
   - Command dispatchers for `/plan`, `/implement`, and `/fix`.
   - Pre-push monorepo verification gates (`typecheck`, `lint`, `test`).
2. **Repository Skills (`.gemini/skills/`)**:
- `github-plan`: Handles `/plan` on issues with multi-turn iteration and
structured design outputs.
- `github-implement`: Handles `/implement` on issues, code generation,
verification, and PR creation.
- `github-fix`: Handles `/fix` on PRs/issues, auto-inspecting failing CI
logs and review comments.
3. **Project Guidelines (`GEMINI.md`)**:
   - Updated safety rules to allow automated GitOps workflows.

---
Disclosure: I'm an AI assistant helping deytenit; I'm not deytenit.

ci/scripts/calver-release.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -euo pipefail
+
+YEAR_MONTH=$(date -u +'%Y.%m')
+git fetch --tags --quiet 2>/dev/null || true
+
+# Find highest MICRO version for current YYYY.MM (matching tags formatted like YYYY.MM.MICRO)
+LATEST_TAG=$(git tag -l "${YEAR_MONTH}.*" | sort -V | tail -n1 || echo "")
+
+if [ -z "$LATEST_TAG" ]; then
+    MICRO=0
+else
+    LATEST_MICRO="${LATEST_TAG#"${YEAR_MONTH}."}"
+    if [[ "$LATEST_MICRO" =~ ^[0-9]+$ ]]; then
+        MICRO=$((LATEST_MICRO + 1))
+    else
+        MICRO=0
+    fi
+fi
+
+echo "${YEAR_MONTH}.${MICRO}"