v1.2.0:7 — add SparkControl AI provider + fix base-URL footgun

SparkControl is a self-hosted local-inference gateway with an OpenAI-compatible API, reached over the internal same-box StartOS address (http://spark-control.startos:9999/v1, plain HTTP). It takes no API key, so generateOpenAIStyle gained a { requireApiKey } option and now omits the Authorization header when no key is set. The Settings form auto-detects the loaded vLLM model via SparkControl's /api/endpoints probe, mirroring the Ollama auto-detect; it's $0 in the cost UI. Custom-URL => admin-only + SSRF-guarded, same as Ollama.

Also fixes a config footgun behind the empty-response report: a custom base URL could ride along to a fixed-URL provider (claude/openai/gemini) whose form field is hidden, get stored, and be silently ignored (the provider always hits its hardcoded endpoint). Both config write paths now null baseUrl for non-custom-URL providers, and the form clears it on provider change.

No schema/data change (AIConfigProfile.provider is free-text). 259 tests pass; built + sideloaded to immense-voyage.local with a clean non-root launch.

docs/guides/ai-subsystem.md

@@ -47,11 +47,34 @@ stores the JSON in the (reused) `parsedProgram` column.
 
 - Each provider yields an async iterable of `GenerateChunk` (`text` / `usage` / `done` /
   `error`); add new ones under `lib/ai/providers/` and register in `index.ts`.
-  `openai.ts` exports both `openai` and `openai-compatible`, so the four provider files
-  register **5** providers (`claude`, `openai`, `openai-compatible`, `gemini`, `ollama`).
+  `openai.ts` exports both `openai` and `openai-compatible`, so the five provider files
+  register **6** providers (`claude`, `openai`, `openai-compatible`, `gemini`, `ollama`,
+  `sparkcontrol`).
+- **SparkControl** (`sparkcontrol.ts`) — the operator's own self-hosted local-inference
+  gateway. OpenAI-compatible wire format, so it reuses `generateOpenAIStyle` with
+  `{ requireApiKey: false }` (keyless on the LAN — the streamer omits the `Authorization`
+  header when no key is set). Reached over the **internal same-box StartOS address**
+  (`http://spark-control.startos:9999/v1`, plain HTTP — no TLS, no cert-skip). Custom base
+  URL ⇒ SSRF-guarded + admin-only, same as Ollama. The Settings UI auto-detects the loaded
+  vLLM model via `app/api/ai/sparkcontrol/model` (probes SparkControl's `/api/endpoints`
+  → `vllm.model`), mirroring the Ollama `/api/tags` auto-detect. Free in the cost UI.
+- **Base-URL hygiene:** only custom-URL providers (`requiresBaseUrl`: ollama,
+  openai-compatible, sparkcontrol) store a base URL. Both config write paths
+  (`configs` POST + `[id]` PATCH) null it for fixed-URL providers, and the Settings form
+  clears it on provider change — otherwise a stale URL silently rides along to
+  claude/openai/gemini, which ignore it and hit their hardcoded endpoints.
 - Streaming AI uses SSE; partial JSON is recovered with `lib/ai/lenientJson.ts`.
 - Pricing/model menus live in `lib/ai/pricing.ts` (`PRICES`, `MODEL_MENU`) — keep them
   paired so every menu model has a price entry (there's a test enforcing this).
+- **Adding a provider** (precedent: `sparkcontrol`, 1.2.0:7) is a fan-out across ~8 spots —
+  miss one and it half-works: the provider file + `ProviderId` union (`types.ts`) + register
+  in `providers/index.ts` (`ALL` + `PROVIDER_ORDER`); the zod `provider` enum in **both**
+  `configs` POST and `[id]` PATCH (+ `defaultName` PRETTY map); the UI `PROVIDERS` list in
+  `AIIntegration.tsx` (`requiresKey`/`requiresUrl` must mirror the server `requiresApiKey`/
+  `requiresBaseUrl`); `MODEL_MENU` (`[]` if no curated menu) + an `estimateCost` branch
+  (free/null for self-hosted). A custom-URL provider is admin-only + SSRF-guarded everywhere
+  (configs POST/PATCH, `ai/test`, any probe route) and must appear in those routes' 403
+  enumeration strings. `ai/test` and `generate` work for free once it's in `getProvider`.
 
 ## SSRF / provider-URL safety