feat: bell-tower favicon, lfx-clean flows, branded HTML mail

backend/components/kirche/README.md

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+# Authoring web forms (CustomInputForm)
+
+Flows that should render a web form start with a `CustomInputForm` node
+(this package — the `kirche` category in the Langflow palette). The API
+derives a JSON Schema + uiSchema from the node's template
+(`app/flows/input_schema.py`) and the webapp renders it with RJSF.
+
+## Adding a new form field
+
+1. Open the Langflow authoring UI (http://localhost:7860) and load the
+   flow from `LANGFLOW_LOAD_FLOWS_PATH` (canonical files are preloaded).
+2. Edit the `CustomInputForm` node: every entry in its `inputs` list is
+   one web-form field. Add an `lfx.io` input, e.g.
+   ```python
+   from lfx.io import DropdownInput
+
+   DropdownInput(
+       name="room",                 # JSON-Schema property key
+       display_name="Room",         # form label (title)
+       info="Where should it take place",  # help text (description)
+       options=["Chapel", "Hall"],  # dropdown choices (enum)
+       value="Chapel",              # prefill (default)
+       required=True,               # marks the field required
+   )
+   ```
+   Supported input types → widgets: `StrInput`/`MessageTextInput` → text,
+   `MultilineInput` → textarea, `SecretStrInput` → password,
+   `IntInput` → integer, `FloatInput` → number, `BoolInput` → checkbox,
+   `DropdownInput` → select, `MultiselectInput` → multi-select,
+   `SliderInput` → slider (needs `range_spec`), `FileInput` → text stub
+   (real upload later).
+3. Add the new field to `collect()` so it reaches the JSON output.
+4. **Wire the envelope**: keep the `ChatInput → form_values` edge (hidden
+   input, `show=False`). Submitted web-form values arrive there as
+   `{"payload": {...}}` and are merged over the defaults. Never make form
+   fields required *with* an incoming edge — that's the envelope's job.
+5. Export the flow (JSON) into `backend/flows/<name>.json` and commit.
+   The API watcher syncs + deploys it automatically; the form schema is
+   regenerated per version.
+
+## Conventions the pipeline relies on
+
+- `required=True` on a template field: `lfx validate --level 4` demands a
+  value or an edge, so the canonical-flow generator
+  (`backend/scripts/make_flow_fixtures.py`) writes a single-space
+  sentinel value for such fields. The form parser treats whitespace-only
+  values as "no default" — don't ship real whitespace defaults.
+- Field key = `name` (stable); label = `display_name`; help = `info`.
+- Unknown future input types degrade to a plain text field in the web
+  form (parser fallback), so adding exotic lfx inputs never breaks runs.
+
+## Regenerating the bundled fixtures
+
+After editing the component source (`form_inputs.py`), refresh the
+canonical + test-fixture exports:
+
+    docker compose exec api /opt/venv/bin/python scripts/make_flow_fixtures.py
+    docker compose exec -T api uv run pytest tests/test_lfx_validate.py