Fix whitespace in periodic summary by inlining albums list

Inline periodic_albums_list computation into periodic_summary_formatted
using {%- -%} whitespace control to prevent unwanted whitespace in the
formatted output. Add documentation about this Jinja2 pattern to CLAUDE.md.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -59,4 +59,32 @@ Zigbee/
 # Author: Alexei Dolgolyov (dolgolyov.alexei@gmail.com)
 ```
 
-When any blueprint file is moved ask if I need to update the link somewhere else.
+When any blueprint file is moved ask if I need to update the link somewhere else.
+
+## Jinja2 Whitespace Issue
+
+Home Assistant evaluates all blueprint variables before conditions are checked. When a variable's Jinja2 template contains whitespace (newlines, indentation), that whitespace gets included in the output even if the template logic produces an empty string.
+
+**Problem:** Using a variable like `{{ my_variable }}` in string replacements will include unwanted whitespace.
+
+**Solution:** Compute complex values inline where they're used, with `{%- -%}` whitespace control:
+
+```yaml
+# BAD - whitespace from my_list variable will be included
+my_list: >
+  {% for item in items %}
+    {{ item }}
+  {% endfor %}
+
+result: "{{ template | replace('{items}', my_list) }}"
+
+# GOOD - inline computation with whitespace control
+result: >
+  {%- set ns = namespace(items = '') -%}
+  {%- for item in items -%}
+    {%- set ns.items = ns.items ~ item -%}
+  {%- endfor -%}
+  {{ template | replace('{items}', ns.items) }}
+```
+
+This pattern is used throughout the Immich Album Watcher blueprint for `common_date`, `common_location`, `video_warning`, and `periodic_albums_list`.