docs(search): scope the relative-offset warning to a value standing alone

The warning said relative offsets such as "-1 week" "in practice mean no
documents at all", unqualified, one bullet after the range-bound rule
offered added:['-1 week' to now] as the example of quoting a bound. Both
sentences were true in their own scope, but read together they talk a
user out of a query that works: the bare value is a zero-width instant,
the same offset as a bound is a real seven-day window (verified:
lo=2026-06-08T12:00, hi=2026-06-15T12:00 from a frozen 2026-06-15T12:00).

Also widens the last sentence to say now-3days and "3 days ago" are
rejected wherever they appear, having checked they are rejected as range
bounds too, single- or double-quoted, not only as bare values.

Restores the 'added:"-1 week"' case to the standalone-forms list, which
the docs name by that exact spelling, and pins the bound reading beside
it so neither half of the warning is an unpinned claim.

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

docs/usage.md

@@ -999,7 +999,7 @@ added:[2005-06-15T09:00:00Z to 2005-06-15T17:00:00Z]
 
 !!! warning
 
-    `now`, `noon`, `midnight` and relative offsets such as `"-3 days"` or `"-1 week"` are accepted by the parser but resolve to a single instant rather than to a span of time, so they match only a document whose timestamp is exactly that instant, which in practice means no documents at all. Quoting does not change this. Spellings like `now-3days` and `"3 days ago"` are rejected outright.
+    As a value on its own, `now`, `noon`, `midnight` and relative offsets such as `"-3 days"` or `"-1 week"` are accepted by the parser but resolve to a single instant rather than to a span of time, so they match only a document whose timestamp is exactly that instant, which in practice means no documents at all. Quoting does not change this. As a *range bound* they are the opposite of a trap and are what you want: `added:['-1 week' to now]` covers the whole of the last seven days. Spellings like `now-3days` and `"3 days ago"` are rejected outright wherever they appear.
 
 #### Searching custom fields
 

src/documents/tests/search/test_documented_syntax.py

@@ -269,6 +269,11 @@ class TestDocumentedDateForms:
             # of the resulting range, not the way the value is delimited.
             'added:"now"',
             'added:"midnight"',
+            # A relative offset, which the warning in the docs names by this
+            # exact spelling. Standing alone it is an instant like the rest of
+            # this list; the same offset used as a range bound is a real
+            # window, pinned by the test below.
+            'added:"-1 week"',
         ],
     )
     def test_forms_the_docs_warn_about_match_nothing(
@@ -298,6 +303,24 @@ class TestDocumentedDateForms:
         assert exc_info.value.field == "added"
         assert exc_info.value.value == "2005-03-"
 
+    def test_relative_offset_as_a_range_bound_is_a_real_window(
+        self,
+        backend: TantivyBackend,
+        dated: dict[str, int],
+    ) -> None:
+        """The same offset that matches nothing on its own spans the last
+        seven days as a lower bound. The docs say so, next to the warning
+        about the standalone form, so both readings are pinned together.
+
+        "last_monday" is indexed at 2026-06-08T10:00, two hours before the
+        window opens, so its exclusion is what shows the bound is the offset
+        and not a whole-day rounding of it.
+        """
+        assert _matched_ids(backend, "added:['-1 week' to now]") == {
+            dated["today"],
+            dated["yesterday"],
+        }
+
     def test_double_quoted_range_bound_is_rejected(
         self,
         backend: TantivyBackend,