fix(view-context): tell the chat agents when not to use it

With the eye on, the snapshot of what the user is looking at was read as
part of the question: asked something unrelated to the open page, the
assistant went investigating the folder with a run of tool calls. The
transport was right; the prompt never said the block can be irrelevant.

New fragment agents/common/view-context.md, included only by the three
type: chat agents. It could have gone in harness.md — which all three
already include — but harness.md is also included by the two memory-lint
agents, which never receive a view. Hence the split, and hence moving the
snapshot bullet there too: both halves of the rule now live in one file.

The rule names the observed behaviour ("never open, list, search or
otherwise investigate ... just because it is there") and keeps the deictic
examples, so curing the over-use does not create the under-use.

docs/ gains the same rule where the in-app assistant reads it; the
CHANGELOG entry for the feature is extended, not duplicated.

CHANGELOG.md

@@ -24,7 +24,9 @@ release PR may merge — and a section is closed at the commit that bumps it.
   work without naming anything; and, on a detail page, which project (and which of its
   tabs), member, connector, plugin, conversation, tool call or LLM request you opened.
   The active section follows you in Tasks, Models, Background agents, the Marketplace
-  search and the mobile app. Like an attachment, what the eye sends goes to the AI
+  search and the mobile app. It is used only when your message is actually about what
+  you have open: asking something unrelated from inside a folder no longer sends the
+  assistant reading through it. Like an attachment, what the eye sends goes to the AI
   provider together with your message — hover it (or tap it) to read exactly what would
   go out, click it to stop sharing; the choice is remembered on this device, and every
   message shows a chip with what it carried. Very long highlights are trimmed, with a