feat: add Pastel color palette generator to Kit stack

Added Pastel service with API and UI to the Kit toolkit:

**New Services:**
- pastel_api: Backend API for color palette generation
  - Image: ghcr.io/valknarness/pastel-api:latest
  - Routes: https://pastel.kit.pivoine.art/api

- pastel_ui: Frontend UI for interactive palette generation
  - Image: ghcr.io/valknarness/pastel-ui:latest
  - Routes: https://pastel.kit.pivoine.art

**Features:**
- Color harmony algorithms
- Interactive palette generation
- Export in various formats
- Programmatic API access
- Path-based routing (UI on root, API on /api)

**Configuration:**
- Updated arty.yml with KIT_PASTEL_* variables
- Updated documentation (CLAUDE.md, README.md)
- Added Traefik labels with SSL, compression, security headers
- Watchtower auto-update enabled

Kit stack now includes 5 services:
- Landing page (kit.pivoine.art)
- Vert file converter (vert.kit.pivoine.art)
- Paint image editor (paint.kit.pivoine.art)
- Pastel color generator (pastel.kit.pivoine.art)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -54,7 +54,7 @@ The **Falcon** is a state-of-the-art containerized starship, powered by Docker's
 | **LINKS** | *Interstellar bookmark archive* | [links.pivoine.art](https://links.pivoine.art) |
 | **VAULT** | *Encrypted password vault* | [vault.pivoine.art](https://vault.pivoine.art) |
 | **JOPLIN** | *Note-taking server & sync hub* | [joplin.pivoine.art](https://joplin.pivoine.art) |
-| **KIT** | *Toolkit hub with converter & editor* | [kit.pivoine.art](https://kit.pivoine.art) |
+| **KIT** | *Toolkit hub with converter, editor & colors* | [kit.pivoine.art](https://kit.pivoine.art) |
 | **JELLY** | *Media streaming server* | [jelly.pivoine.art](https://jelly.pivoine.art) |
 | **DROP** | *Peer-to-peer file sharing* | [drop.pivoine.art](https://drop.pivoine.art) |
 | **RESTIC** | *Automated backup vault system* | [restic.pivoine.art](https://restic.pivoine.art) |
@@ -222,6 +222,16 @@ arty env/sync
 # - Filters, drawing tools, text, shapes
 # - Supports PNG, JPG, GIF, WebP
 # - Client-side processing (no uploads)
+
+# Color Palette Generator (Pastel)
+# URL: https://pastel.kit.pivoine.art
+# API: https://pastel.kit.pivoine.art/api
+# Features:
+# - Generate beautiful color palettes
+# - Color harmony algorithms
+# - Interactive palette generation
+# - Export in various formats
+# - Programmatic API access
 ```
 
 ### Backup Operations (RESTIC System)
@@ -278,7 +288,7 @@ THE FALCON (falcon_network)
 │  ├─ Linkwarden Marks   [links.pivoine.art]
 │  ├─ Vaultwarden Vault  [vault.pivoine.art]
 │  ├─ Joplin Sync Server [joplin.pivoine.art]
-│  ├─ Kit Toolkit        [vert.kit.pivoine.art, paint.kit.pivoine.art]
+│  ├─ Kit Toolkit        [vert.kit.pivoine.art, paint.kit.pivoine.art, pastel.kit.pivoine.art]
 │  ├─ Jellyfin Media     [jelly.pivoine.art]
 │  ├─ PairDrop Sharing   [drop.pivoine.art]
 │  ├─ Backrest Backups   [restic.pivoine.art]