feat(scripts): fold generate-secrets.sh into update.sh, auto-mint virtual keys

update.sh now creates .env from .env.example if missing, idempotently fills
in every random secret (same logic generate-secrets.sh had, now removed),
resolves SEARXNG_LAN_IP from search.home via the host's own DNS, and mints
OPENWEBUI_LITELLM_KEY / MEMORY_RETRIEVAL_EMBEDDING_KEY through LiteLLM's own
/key/generate API once litellm is up — no more manual Admin UI step for the
stack's own two workload keys. Docs updated to point at update.sh as the
one command; docs/proxy-key-onboarding.md keeps the manual/API steps as the
fallback and for onboarding other workloads.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/proxy-key-onboarding.md

@@ -2,6 +2,8 @@
 
 How to issue a new per-workload API key against the LiteLLM proxy (see [issue #10](https://git.arthurerlich.de/haylan/LLM-Server/issues/10) / `docs/research/proxy-tool-choice.md`), so a new workload (a code-reviewer tool, Paperless-OCR, Gitea code review, etc.) gets its own key and its own visible usage/spend.
 
+`OPENWEBUI_LITELLM_KEY` and `MEMORY_RETRIEVAL_EMBEDDING_KEY` — the two keys this stack's own services need — are minted automatically by `./scripts/update.sh` via the same API `curl` shows below; the steps here are for any other workload, or for those two if the automatic mint ever fails.
+
 ## Create the key
 
 1. Log into LiteLLM's Admin UI (`/ui` on the proxy's deployed URL).
@@ -9,6 +11,16 @@ How to issue a new per-workload API key against the LiteLLM proxy (see [issue #1
 3. Name it `<workload>-<purpose>` — a short slug matching the workload, e.g. `paperless-ocr`, `gitea-code-review`, `openwebui`. This name is the ledger: LiteLLM's dashboard lists keys by name, so there's no separate tracking doc to keep in sync — name it clearly and the Usage tab tells you the rest (spend, last used, etc.).
 4. Leave budget and rate limits unset (unlimited) by default. This is a shadow-cost estimate for fun, not real accounting or resource protection — see `docs/research/proxy-shadow-pricing.md`. Only set a budget if a specific workload turns out to need a tripwire.
 
+Or the same thing over the API (what `update.sh` does):
+
+```bash
+curl -sf -X POST "http://<proxy>:4000/key/generate" \
+  -H "Authorization: Bearer ${LITELLM_MASTER_KEY}" \
+  -H "Content-Type: application/json" \
+  -d '{"key_alias": "<workload>-<purpose>"}'
+# -> {"key": "sk-...", ...}
+```
+
 ## Hand it to the workload
 
 Drop the key into that workload's own `.env` (or equivalent config) — never into this repo. Each workload's config is the source of truth for its own credential, same pattern as `.env.example` in this repo for the existing stack.