feat: first cut on M0 - base structure of project

docs/LIQUID_FEATURE_INVENTORY.md

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+# bDS Liquid Feature Inventory
+
+Inventoried from the 12 default templates in the TypeScript app (`src/main/engine/templates/`).
+
+## Template Files Analyzed
+
+1. `single-post.liquid` (main)
+2. `post-list.liquid` (main)
+3. `not-found.liquid` (main)
+4. `macros/gallery.liquid`
+5. `macros/youtube.liquid`
+6. `macros/vimeo.liquid`
+7. `macros/photo-archive.liquid`
+8. `macros/tag-cloud.liquid`
+9. `partials/head.liquid`
+10. `partials/menu.liquid`
+11. `partials/menu-items.liquid`
+12. `partials/language-switcher.liquid`
+
+## Tags Used
+
+| Tag | Used In |
+|---|---|
+| `if` / `endif` | 9 templates |
+| `elsif` | post-list |
+| `else` | 7 templates |
+| `for` / `endfor` | 7 templates |
+| `assign` | 4 templates (not-found, post-list, head, single-post) |
+| `render` | 5 templates (menu, menu-items, not-found, post-list, single-post) |
+
+### NOT Used
+
+`unless`, `case/when`, `capture`, `layout`, `include`, `comment`, `raw`, `increment`, `decrement`, `tablerow`, `cycle`
+
+## Filters Used
+
+| Filter | Type | Signature |
+|---|---|---|
+| `escape` | Built-in | `\| escape` |
+| `default` | Built-in | `\| default: value` |
+| `append` | Built-in | `\| append: string` |
+| `url_encode` | Built-in | `\| url_encode` |
+| `i18n` | **Custom** | `\| i18n: language` — translation lookup by key and language |
+| `markdown` | **Custom** | `\| markdown: post.id, post_data_json_by_id, canonical_post_path_by_slug, canonical_media_path_by_source_path, language, language_prefix` — markdown-to-HTML with macro expansion and link resolution (6 args) |
+
+### NOT Used
+
+`date`, `truncate`, `split`, `join`, `where`, `group_by`, `map`, `sort`, `reverse`, `size` (as pipe filter), `strip`, `strip_html`, `downcase`, `upcase`, `replace`, `remove`, `first`, `last`, `abs`, `ceil`, `floor`, `round`, `plus`, `minus`, `times`, `divided_by`, `modulo`
+
+## Operators
+
+| Operator | Example |
+|---|---|
+| `==` | `item.href == '#'`, `archive_context.kind == 'tag'` |
+| `>` | `menu_items.size > 0`, `blog_languages.size > 1` |
+| `and` | `menu_items and menu_items.size > 0` |
+| `or` | `archive_context.kind == 'tag' or archive_context.kind == 'category'` |
+| `blank` | `canonical_post_href == blank` (nil/empty check) |
+| bare truthiness | `{% if html_theme_attribute %}`, `{% if caption %}` |
+
+### NOT Used
+
+`!=`, `<`, `<=`, `>=`, `contains`
+
+## Property Access Patterns
+
+| Pattern | Examples |
+|---|---|
+| Dot notation | `archive_context.kind`, `post.title`, `item.media_path`, `lang.is_current` |
+| `.size` property | `menu_items.size`, `items.size`, `post_categories.size` |
+| Bracket notation (hash/map lookup) | `canonical_post_path_by_slug[post.slug]`, `tag_color_by_name[tag]` |
+
+## Whitespace Stripping
+
+`{%- -%}` used in 3 macro templates only: `photo-archive`, `gallery`, `tag-cloud`.
+
+## For-Loop Features
+
+| Feature | Used? |
+|---|---|
+| Basic `for x in collection` | YES |
+| Nested `for` loops | YES (photo-archive, post-list) |
+| Recursive `render` in loop | YES (menu-items renders itself for children) |
+| `forloop.first` / `forloop.last` | NO |
+| `limit` / `offset` | NO |
+| `reversed` | NO |
+
+## Render Tag Usage
+
+- Uses named parameter passing: `{% render 'partials/menu-items', items: menu_items, include_calendar: true, language: language %}`
+- Recursive self-render: menu-items calls `render 'partials/menu-items'` for nested children
+- Partial paths use forward-slash notation: `'partials/head'`, `'partials/menu'`
+
+## Two-Step Dynamic i18n Keys
+
+`{% assign month_key = 'render.month.' | append: archive_context.month %}` then `{{ month_key | i18n: language }}`
+
+## Scope Summary
+
+The Rust Liquid implementation needs approximately **35% of the full specification**:
+
+- **Tags**: `if`/`elsif`/`else`, `for`, `assign`, `render` (not `include`)
+- **Built-in filters**: `escape`, `default`, `append`, `url_encode`
+- **Custom filters**: `i18n` (key + language), `markdown` (content + 6 args)
+- **Operators**: `==`, `>`, `and`, `or`, truthiness, `blank`
+- **Access**: dot notation, `.size` property, bracket notation for hash/map lookups
+- **Whitespace stripping**: `{%- -%}` support required