feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/fluxer_docs/resources/themes.mdx

@@ -0,0 +1,29 @@
+---
+title: 'Themes'
+description: 'Themes object schemas from the Fluxer API.'
+---
+
+<a id="themecreaterequest"></a>
+
+## ThemeCreateRequest
+
+**Related endpoints**
+
+- [`POST /users/@me/themes`](/api-reference/themes/create-theme)
+
+| Field | Type | Description |
+|-------|------|-------------|
+| css | string | CSS text to store and share |
+
+<a id="themecreateresponse"></a>
+
+## ThemeCreateResponse
+
+**Related endpoints**
+
+- [`POST /users/@me/themes`](/api-reference/themes/create-theme)
+
+| Field | Type | Description |
+|-------|------|-------------|
+| id | [SnowflakeType](#snowflaketype) | The unique identifier for the created theme |
+