Add Git auto-sync for multi-device vault syncing

GIT-SYNC.md

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+# Git Auto-Sync Setup for Second Brain
+
+Automatically sync vault changes between server, desktop, and phone using Git.
+
+## How It Works
+
+```
+Desktop/Phone Changes → Git Repo ← Server Auto-Commits
+        ↓
+   All devices sync
+```
+
+## Server Setup
+
+### 1. Install Auto-Sync Service
+
+```bash
+sudo cp /workspace/second-brain/git-auto-sync.service /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable git-auto-sync.service
+sudo systemctl start git-auto-sync.service
+
+# Verify
+sudo systemctl status git-auto-sync.service
+```
+
+### 2. Watch Auto-Commits
+
+```bash
+# View logs
+sudo journalctl -fu git-sync
+
+# Example output:
+# [2026-04-26 07:45:30] Changes detected:
+#   M  03-learnings/architecture.md
+#   A  00-inbox/new-idea.md
+#   ✓ Committed
+#   ✓ Pushed to remote
+```
+
+## Desktop Setup
+
+### 1. Clone the Vault
+
+```bash
+# First time
+git clone ssh://user@server:/workspace/second-brain ~/Obsidian/second-brain
+
+# Or if using Local Sync, configure it to pull from this git repo
+```
+
+### 2. Pull Latest Changes
+
+```bash
+cd ~/Obsidian/second-brain
+git pull
+```
+
+### 3. Auto-Pull (Optional)
+
+**macOS/Linux:**
+```bash
+# Add to crontab (every 5 minutes)
+crontab -e
+*/5 * * * * cd ~/Obsidian/second-brain && git pull -q 2>/dev/null
+```
+
+**Or use a Git hook:**
+```bash
+cat > .git/hooks/post-merge << 'EOF'
+#!/bin/bash
+# Auto-sync after merge
+echo "✓ Vault synced"
+EOF
+chmod +x .git/hooks/post-merge
+```
+
+## Phone Setup
+
+### With Obsidian + Local Sync Plugin
+
+1. **On Server:**
+   - Make sure git repo is accessible (or use Gitea)
+
+2. **On Phone:**
+   - Install "Local Sync" plugin in Obsidian
+   - Configure it to sync with: `ssh://user@server:/workspace/second-brain`
+   - Or configure with Gitea URL
+
+3. **On Desktop:**
+   - Same setup, pull regularly
+
+---
+
+## Sync Strategies
+
+### Strategy 1: Git-Only (Recommended)
+
+- Server auto-commits all changes
+- Desktop: `git pull` manually or via cron
+- Phone: Local Sync pulls from server git
+
+```bash
+# Desktop cron (every 5 min)
+*/5 * * * * cd ~/Obsidian/second-brain && git pull -q
+```
+
+### Strategy 2: Obsidian + Local Sync
+
+- Desktop + Phone: Use Obsidian's Local Sync plugin
+- Server: Git auto-sync mirrors changes
+
+**Advantage:** Real-time sync on devices, server keeps git history
+
+### Strategy 3: Git + SSH Pull
+
+- Desktop/Phone: SSH git clone
+- Pull before opening Obsidian
+- Push changes after editing
+
+```bash
+#!/bin/bash
+# pre-open-obsidian.sh
+cd ~/Obsidian/second-brain
+git pull
+open ~/Obsidian/second-brain  # macOS
+```
+
+---
+
+## Remote Repository (Gitea / GitHub)
+
+### Configure Remote Push
+
+**If using Gitea on your server:**
+
+```bash
+# On server
+cd /workspace/second-brain
+git remote add gitea ssh://git@gitea-server/your-repo.git
+
+# Verify
+git remote -v
+
+# Push existing commits
+git push -u gitea master
+```
+
+**Then on desktop/phone:**
+
+```bash
+git clone ssh://git@gitea-server/your-repo.git
+```
+
+---
+
+## Monitoring Syncs
+
+### View Recent Commits
+
+```bash
+cd /workspace/second-brain
+git log --oneline -10
+```
+
+### Check Sync Status
+
+```bash
+# See what's staged but not committed
+git status
+
+# See changes in last hour
+git log --since="1 hour ago" --oneline
+```
+
+### Manual Sync Test
+
+```bash
+# On desktop: make a change
+echo "test" >> 00-inbox/test.md
+git add .
+git commit -m "Test sync"
+git push
+
+# On server: should auto-pull (if configured)
+cd /workspace/second-brain
+git log --oneline -1
+```
+
+---
+
+## Conflict Resolution
+
+If both server and desktop edit the same file:
+
+```bash
+# Server (auto-sync) will get it first
+# Desktop pulls and sees conflict marker:
+
+<<<<<<< HEAD
+desktop version
+=======
+server version
+>>>>>>> origin/master
+
+# Manually resolve, then:
+git add .
+git commit -m "Resolved conflict"
+git push
+```
+
+---
+
+## Disable Auto-Sync (if needed)
+
+```bash
+sudo systemctl stop git-auto-sync.service
+sudo systemctl disable git-auto-sync.service
+```
+
+---
+
+## Performance Notes
+
+- **Poll interval:** 30 seconds (adjustable)
+- **Commit overhead:** ~50ms per check
+- **Memory:** ~64MB (limited)
+- **CPU:** ~10% max
+
+---
+
+Created: 2026-04-26