feat: add label-based reconciliation pause support

[veerendra2]

Summary

Add support for pausing reconciliation on specific stacks using a label. When a stack has the label composeflux.reconciliation.pause=true, ComposeFlux will skip all reconciliation operations for that stack.

Key feature: Add the label via Docker CLI without modifying Git - perfect for temporary operations like backups.

Problem (Fixes #22)

During database backups (e.g., Kopia backing up PostgreSQL), containers must stay stopped. ComposeFlux should not touch these stacks during reconciliation to prevent data corruption.

Solution

Add a label-based pause mechanism that completely excludes stacks from reconciliation:

• Label: composeflux.reconciliation.pause=true
• Behavior: Stack is skipped in all reconciliation operations:
  • ✅ No deployment during Sync()
  • ✅ No image updates during SyncImages()
  • ✅ No pruning even if deleted from Git

Usage

Recommended: Docker CLI (no Git changes)

# Pause reconciliation for a stack
for container in $(docker ps -aq --filter "label=com.docker.compose.project=immich"); do
  docker container update --label-add composeflux.reconciliation.pause=true $container
done

# Resume reconciliation
for container in $(docker ps -aq --filter "label=com.docker.compose.project=immich"); do
  docker container update --label-rm composeflux.reconciliation.pause $container
done

Example: Backup workflow

# 1. Pause reconciliation
for container in $(docker ps -aq --filter "label=com.docker.compose.project=immich"); do
  docker container update --label-add composeflux.reconciliation.pause=true $container
done

# 2. Stop container for backup
docker stop immich-postgres-1

# 3. Run backup
kopia snapshot create /var/lib/postgresql/data

# 4. Resume reconciliation and restart
for container in $(docker ps -aq --filter "label=com.docker.compose.project=immich"); do
  docker container update --label-rm composeflux.reconciliation.pause $container
done
docker start immich-postgres-1

Alternative: Compose file (permanent pause)

name: immich
labels:
  composeflux.reconciliation.pause: "true"
services:
  postgres:
    image: postgres:16

Changes

• Add LabelReconciliationPause constant
• Add isReconciliationPaused() helper function
• Check pause label in Sync(), SyncImages(), and Prune()
• Log when stacks are skipped due to pause label
• Add documentation with Docker CLI examples

Files Changed

• internal/reconcile/deploy.go - Add label constant
• internal/reconcile/prune.go - Add helper function, skip paused stacks
• internal/reconcile/sync.go - Skip paused stacks in sync and image updates
• docs/Introduction.md - Document pause label feature
• docs/index.md - Add GitHub badge

🤖 Generated with Claude Code

[veerendra2]

Closing this PR. After testing, simply disabling ContainerPrune is sufficient to solve the issue. The label-based pause feature is not needed. See #26 for the simpler solution.