feat(registry): add generate-registry.sh script and docs

Shell script reads .pkg ZIPs, extracts manifests, and emits a
registry.json for self-hosted package discovery. Docs cover the
JSON format, admin config, and self-hosting setup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/PACKAGE-REGISTRY.md

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+# Package Registry
+
+The package registry lets admins browse and install packages from an external
+JSON index — a lightweight alternative to manually uploading `.pkg` files.
+
+## Registry JSON Format
+
+The registry is a static JSON file matching the `RegistryResponse` struct:
+
+```json
+{
+  "packages": [
+    {
+      "id": "notes",
+      "title": "Notes",
+      "version": "0.8.0",
+      "description": "Markdown notes with backlinks and graph view",
+      "author": "switchboard",
+      "type": "extension",
+      "tier": "core",
+      "download_url": "https://cdn.example.com/pkg/notes.pkg",
+      "size": 48200,
+      "updated_at": "2026-03-20T00:00:00Z"
+    }
+  ]
+}
+```
+
+### Required Fields
+
+| Field          | Description                                    |
+|----------------|------------------------------------------------|
+| `id`           | Package identifier (matches `manifest.json`)   |
+| `title`        | Display name                                   |
+| `version`      | Semver version string                          |
+| `description`  | Short description                              |
+| `download_url` | HTTPS URL to the `.pkg` file (must be HTTPS)   |
+
+### Optional Fields
+
+| Field        | Description                              |
+|--------------|------------------------------------------|
+| `author`     | Package author                           |
+| `type`       | `extension` or `library`                 |
+| `tier`       | `core`, `official`, or `community`       |
+| `size`       | File size in bytes                       |
+| `updated_at` | ISO 8601 timestamp of last update        |
+
+## Configuring the Registry URL
+
+### Via Admin UI
+
+Navigate to **Admin > Settings > Package Registry** and enter the registry URL.
+
+### Via API
+
+```bash
+curl -X PUT /api/v1/admin/settings/package_registry \
+  -H "Content-Type: application/json" \
+  -d '{"value": {"url": "https://cdn.example.com/pkg/registry.json"}}'
+```
+
+## Generating a Registry
+
+Use `scripts/generate-registry.sh` to build a `registry.json` from a
+directory of `.pkg` files:
+
+```bash
+# Default: reads dist/, uses placeholder base URL
+./scripts/generate-registry.sh
+
+# Custom directory and base URL
+./scripts/generate-registry.sh ./my-packages https://cdn.example.com/pkg > registry.json
+```
+
+Requirements: `jq`, `unzip`, and `stat` (GNU or BSD).
+
+## Self-Hosting
+
+Any HTTPS-capable file server works. Upload your `.pkg` files and the
+generated `registry.json` to the same directory, then point the admin
+setting to the `registry.json` URL.
+
+Example with a static file server:
+
+```
+/var/www/packages/
+  registry.json
+  notes.pkg
+  chat.pkg
+  chat-core.pkg
+```
+
+The registry is fetched and cached for 5 minutes on each browse request.

scripts/generate-registry.sh

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+#!/usr/bin/env bash
+# generate-registry.sh — Build a registry.json from a directory of .pkg files.
+#
+# Usage:
+#   ./scripts/generate-registry.sh [PKG_DIR] [BASE_URL]
+#
+# Arguments:
+#   PKG_DIR   Directory containing .pkg files (default: dist/)
+#   BASE_URL  HTTPS base URL for download links (default: https://example.com/packages)
+#
+# Output:
+#   Writes registry.json to stdout. Redirect to a file:
+#     ./scripts/generate-registry.sh dist/ https://cdn.example.com/pkg > registry.json
+
+set -euo pipefail
+
+PKG_DIR="${1:-dist}"
+BASE_URL="${2:-https://example.com/packages}"
+
+# Strip trailing slash
+BASE_URL="${BASE_URL%/}"
+
+if [ ! -d "$PKG_DIR" ]; then
+    echo "Error: directory '$PKG_DIR' not found" >&2
+    exit 1
+fi
+
+# Collect entries
+entries=()
+
+for pkg in "$PKG_DIR"/*.pkg; do
+    [ -f "$pkg" ] || continue
+
+    # Extract manifest.json from the ZIP archive
+    manifest=$(unzip -p "$pkg" manifest.json 2>/dev/null) || {
+        echo "Warning: skipping $pkg (no manifest.json)" >&2
+        continue
+    }
+
+    # Read fields from manifest
+    id=$(echo "$manifest"          | jq -r '.id // empty')
+    title=$(echo "$manifest"       | jq -r '.title // .id')
+    version=$(echo "$manifest"     | jq -r '.version // "0.0.0"')
+    description=$(echo "$manifest" | jq -r '.description // ""')
+    author=$(echo "$manifest"      | jq -r '.author // ""')
+    type=$(echo "$manifest"        | jq -r '.type // "extension"')
+    tier=$(echo "$manifest"        | jq -r '.tier // "community"')
+
+    if [ -z "$id" ]; then
+        echo "Warning: skipping $pkg (no id in manifest)" >&2
+        continue
+    fi
+
+    filename=$(basename "$pkg")
+    size=$(stat -c%s "$pkg" 2>/dev/null || stat -f%z "$pkg" 2>/dev/null || echo 0)
+    updated_at=$(date -r "$pkg" -u +"%Y-%m-%dT%H:%M:%SZ" 2>/dev/null || date -u +"%Y-%m-%dT%H:%M:%SZ")
+
+    entry=$(jq -n \
+        --arg id "$id" \
+        --arg title "$title" \
+        --arg version "$version" \
+        --arg description "$description" \
+        --arg author "$author" \
+        --arg type "$type" \
+        --arg tier "$tier" \
+        --arg download_url "$BASE_URL/$filename" \
+        --argjson size "$size" \
+        --arg updated_at "$updated_at" \
+        '{id: $id, title: $title, version: $version, description: $description,
+          author: $author, type: $type, tier: $tier, download_url: $download_url,
+          size: $size, updated_at: $updated_at}')
+
+    entries+=("$entry")
+done
+
+# Build final JSON
+if [ ${#entries[@]} -eq 0 ]; then
+    echo '{"packages": []}' | jq .
+else
+    printf '%s\n' "${entries[@]}" | jq -s '{packages: .}'
+fi