docs(757): enumerate all seven filler kinds, and record why the two query tests compose

Round-3 review found one statement in the PR that was not true of the code:
showFiller's description named four of FillerKind's seven non-None values
(pre/mid/post-roll, tail), omitting Fallback, GuideMode and DecoDefault. The
handler filters `ShowFiller || FillerKind == None`, so it excludes ALL of them,
and an agent debugging a missing Fallback or Deco item would not have found it
in that list. Verified against Core/Domain/Filler/FillerKind.cs.

Also records the anti-vacuity argument the reviewer surfaced, which was the
strongest one in this PR and was going unstated: the pre-existing
Every_Query_Parameter_Should_Be_A_Declared_Property filters on
`QueryParameters is { Count: > 0 }` -- a filter on the very property it asserts
-- so a tool that lost its query parameters escaped it entirely. That is
precisely how list_playouts and get_playout_items hid. The new unfiltered test
reports them as unreachable and the old one checks the routed-vs-declared half;
neither subsumes the other, which is why the inner duplicate was removed rather
than kept.

Decisions-Edit: yes

ErsatzTV.Mcp/ToolCatalog.cs

@@ -50,7 +50,8 @@ public static class ToolCatalog
             [
                 Bool(
                     "showFiller",
-                    "Include filler items (pre/mid/post-roll, tail) in the result; default false returns only non-filler items.",
+                    "Include items whose filler kind is not None (pre/mid/post-roll, tail, fallback, guide-mode, deco); "
+                    + "default false returns only non-filler items.",
                     arg: In.Query),
                 .. Page()
             ]),

docs/decisions/records/mcp/tool-schema-openapi-parity.md

@@ -64,6 +64,14 @@ the same shape with paging). That test **accumulates** its mismatches and assert
 reports the whole drift set — failing on the first would invite fixing one tool at a time, which is
 how the twin in this very issue stayed hidden.
 
+It also **composes with** the older `Every_Query_Parameter_Should_Be_A_Declared_Property`, and the pair
+is the clearest illustration in this repo of why "a test that filters on the property it asserts cannot
+see what is missing" is a rule. That older test filters `Where(t => t.QueryParameters is { Count: > 0 })`
+— so a tool that lost its query parameters entirely escaped it, which is exactly how `list_playouts` and
+`get_playout_items` hid. The new test has no filter and reports them as *unreachable*; the old one then
+checks that a routed parameter is also a declared argument. Neither subsumes the other, and the inner
+duplicate of the old check was deliberately removed from the new test rather than kept as a second copy.
+
 **Scope, stated so it is not mistaken for more.** Request bodies are compared for POST/PUT/PATCH only.
 DELETE is uncovered because `ErsatzTvApiClient` builds a body for POST/PUT/PATCH only, so a body
 argument on a DELETE tool would be silently dropped; no tool has one today. Header arguments (`ifMatch`)