fix(booth): put the blur toggle on every item kind, and make it look like a control

The operator asked "no UI option to blur/unblur?" and was right twice over.

MISSING ENTIRELY ON TWO OF THREE BRANCHES. booth.html renders docs, media and
everything-else through separate <figure> blocks. The toggle went into the
media branch only, so inline docs -- the branch that puts readable text straight
on the page, the one that needs blur most -- had no control at all, and `other`
files only got a caption row if they happened to carry a caption.

This is the SECOND time this feature shipped having patched some branches and
not others; the blurred class itself had the same gap one commit ago. So the
toggle is now a single Jinja macro called from all three sites, which makes
"patched two of three" impossible rather than merely unlikely, and
test_every_item_kind_gets_exactly_one_blur_toggle counts toggles against figures
across mixed kinds so a fourth branch cannot quietly skip it.

INVISIBLE WHERE IT DID RENDER. v1 was a bare `◌` at 0.78rem in --muted with no
border, no label and no hover affordance. It now reads `◌ blur` / `◉ blurred`
with a border, matching the other per-item controls. A control nobody can find
is a control that is not there.

Docs get it in the doc bar beside ⤢ ⬇ ✕, with stopPropagation so submitting it
does not collapse the <details> it lives inside.

Verified live on all three kinds: 3 figures, 3 toggles, and the POST round trip
blurs and un-blurs. 167 tests pass.

README.md

@@ -52,7 +52,17 @@ booth blur   <name> <file>...     # hide from a glance
 booth unblur <name> <file>...
 ```
 
-Or the ◌ / ◉ toggle in each item's caption row on the booth page.
+Or the **`◌ blur` / `◉ blurred`** button on every item in the booth page —
+in the caption row for images, video, audio and plain files, and in the doc bar
+beside ⤢ ⬇ ✕ for inline docs.
+
+⚠ The toggle is emitted by ONE Jinja macro (`blurtoggle`) called from all three
+item branches. booth.html renders docs, media and everything-else through
+separate `<figure>` blocks, and this feature was twice shipped having patched
+only some of them — first the blur class, then the toggle itself. Add a fourth
+branch and you must call the macro from it;
+`test_every_item_kind_gets_exactly_one_blur_toggle` counts toggles against
+figures across mixed kinds and will fail if you don't.
 
 - **State** is `.blurred` in the booth dir — one booth-relative item path per
   line, the same filesystem-is-the-state idiom as `.pins` and `.forever`. An