feat(searxng): enable the keyed braveapi engine

Brave Search API key wired literally into the settings file and committed.
Operator decision, 2026-09-18, made explicitly: this is a free-tier key on a
rate-limited service of marginal value — "if the service is useless, so is the
key" — so it does not justify the machinery that keeping it out of git would
cost. The key remains in the vault at nh3-docker/searxng-brave-api-key as
well. This is a scoped judgement about one low-value credential and not a
change to the no-secrets-in-git rule for anything else.

⚠ It cannot be un-committed. Rotation means issuing a new key at Brave and
replacing the line; never a history rewrite, since the repo is shared and
other sessions commit to it.

There is no supported alternative in this build. An earlier attempt used
`api_key: !ENV SEARXNG_BRAVE_API_KEY`, which crash-looped the container ten
times with search down fleet-wide: the settings loader has no !ENV YAML
constructor, reads only SEARXNG_SETTINGS_PATH from the environment, and the
entrypoint substitutes only `ultrasecretkey` at template-creation time. The
variable reaches the container and is never read. Literal or nothing.

Key verified against Brave's API directly before wiring, and verified in place
after: three consecutive queries returned 55-63 results from six engines with
braveapi contributing 20 each time, while google cse and marginalia remain
quota-suspended. General web engines are now seven, up from one this morning.

stacks/searxng/conf/searxng-settings.yml

@@ -64,14 +64,26 @@ use_default_settings:
 # hardcode). A GLM web-search engine is possible as a custom JSON engine but
 # needs a z.ai/bigmodel search key — not in the vault as of today.
 engines:
-  # ⚠ infra-ops 2026-09-18 12:56: the block below was commented out to stop a
-  # crash-loop. This searxng build has no !ENV YAML constructor, so the file
-  # failed to parse and the container restarted 10 times with search down
-  # fleet-wide. Original preserved at searxng-settings.yml.inflight-20260918-1252.
-  # Inline the key or load it another way; !ENV is not supported here.
-  # - name: braveapi
-  #   api_key: !ENV SEARXNG_BRAVE_API_KEY
-  #   inactive: false
+  # ⚠ THE KEY BELOW IS COMMITTED ON PURPOSE. Operator decision, 2026-09-18:
+  # this is a free-tier Brave Search API key on a rate-limited service of
+  # marginal value — "if the service is useless, so is the key" — so it is not
+  # worth the machinery that keeping it out of git would cost. Do not treat
+  # this as licence for other credentials; everything else goes in the vault
+  # (this key is also at nh3-docker/searxng-brave-api-key).
+  #
+  # ⚠ It cannot be un-committed. Rotation means issuing a NEW key at Brave and
+  # replacing this line, never rewriting history — the repo is shared and
+  # other sessions commit to it.
+  #
+  # An earlier attempt used `api_key: !ENV SEARXNG_BRAVE_API_KEY`. This build
+  # has no !ENV YAML constructor, so the file failed to parse and the container
+  # crash-looped ten times with search down fleet-wide. There is no env-var
+  # path into this file: the loader reads only SEARXNG_SETTINGS_PATH, and the
+  # entrypoint substitutes only `ultrasecretkey`. Literal or nothing.
+  - name: braveapi
+    api_key: BSAa55OlyBPDjHcvyRiOcBl5USayGXb
+    disabled: false
+    inactive: false
   - name: marginalia
     api_key: public
     disabled: false