feat: add deepsearch research system with CLI prune/clear and database schema

Implement a multi-agent deep web research subsystem including CLI commands for pruning expired jobs and clearing all artifacts, database tables for sessions/messages/URL cache with indexes, config paths for chroma storage, and internal embed URL for vector operations.

README.md

@@ -242,7 +242,7 @@ and its full configuration are documented automatically - including future servi
 - **`ServiceManager`** - singleton: `register`, `describe_all`, `set_enabled`, `send_command`, `save_config`, `supervise`, `shutdown_all`
 - **`NewsService`** - fetches news from `news.app.molodetz.nl/api`, grades with AI, stores articles >= threshold
 - **`BotsService`** - Playwright fleet of AI personas that browse and interact with a DevPlace instance, with live cost/usage metrics (opt-in; install the `bots` extra)
-- **`GatewayService`** - OpenAI-compatible LLM gateway at `/openai/v1/*`, forwarding to DeepSeek (default) with optional vision augmentation; the single point of truth for AI that every other service routes through (enabled by default)
+- **`GatewayService`** - OpenAI-compatible LLM gateway at `/openai/v1/*`, forwarding to DeepSeek (default) with optional vision augmentation; the single point of truth for AI that every other service routes through (enabled by default). Every chat request is made date-aware by injecting the current date in EU `DD/MM/YYYY` format into the system message when it contains no date already (date only, never time, to keep upstream prompt caching effective), and an admin-configurable system preamble (`gateway_system_preamble`) can be prepended ahead of the client's system message on every call
 - **`JobService` / `ZipService` / `ForkService`** - generic async job framework (`services/jobs/`) for heavy, blocking work run off the request path; `ZipService` builds project zip archives in a subprocess, `ForkService` copies a project into a new project owned by the forking user
 - **`ContainerService`** - the admin container manager (`services/containers/`): a reconciling supervisor for container instances, all running one shared prebuilt image
 
@@ -374,7 +374,7 @@ Configuration on the Services tab:
 | `gateway_instances` | `4` | Max concurrent upstream forwards per worker (pool + semaphore) |
 | `gateway_timeout` | `300` | Upstream timeout (seconds); minimum five minutes; also bounds the vision describe-image call |
 | `gateway_vision_enabled` / `_url` / `_model` / `_key` / `_cache_size` | on / OpenRouter / Gemma / env / 256 | Image-description augmentation |
-| `gateway_embed_enabled` / `_url` / `_model` / `_key` | on / OpenRouter / Qwen3 8B / migrated | Embeddings at `/openai/v1/embeddings` (client model `molodetz~embed`) |
+| `gateway_embed_enabled` / `_url` / `_model` / `_key` | on / OpenRouter / Qwen3 8B / vision-key fallback | Embeddings at `/openai/v1/embeddings` (client model `molodetz~embed`) |
 | `gateway_require_auth` | on | When off, the gateway is open |
 | `gateway_allow_admins` / `gateway_allow_users` | on / off | Which DevPlace users may call it (any auth scheme) |
 | `gateway_access_key` | empty | A standalone key (sent as `X-API-KEY`/Bearer) that always grants access |