feat(ssr): migrate location-select to a Selmer template (Phase 2 — Selmer validated)

First interactive Transaction Edit component rendered from a Selmer template instead of
Hiccup/com/select, proving the render-file path + the Hiccup<->Selmer interop bridge on
real, e2e-covered markup.

- resources/templates/components/location-select.html: plain-HTML <select> with a
  {% for %} over option maps + {% if opt.selected %}.
- location-select*: build options/selected/classes in Clojure (reusing
  inputs/default-input-classes so styling can't drift), render via
  sel/render->hiccup, and embed the fragment back into the still-Hiccup account row.
- skill: finalize selmer-conventions.md from this validated example (was a stub); add the
  cookbook entry; scorecard marks the first Selmer component.

Verified on a fresh server: full suite 38 pass / 1 unrelated fail, swap 6/6,
transaction-edit 8/8 -- the Shared Location test selects through the Selmer <select>,
saves, and spreads Shared -> DT. Verified by string-match + e2e (not byte-parity:
hh/add-class is set-based so class order differs, CSS is order-independent).

Scope note: the modal's remaining attribute-heavy components delegate to the shared
com/typeahead / com/select / com/button-group-button; converting those is the
cross-cutting Phase 11 Selmer sweep, not a single-modal change (Open decision 2).

.claude/skills/ssr-form-migration/reference/component-cookbook.md

@@ -90,6 +90,25 @@ replaces the amount input (caret survives).
                  :placeholder "Optional note"})   ; no hx-* — rides along to save
 ```
 
+## location-select — first Selmer-migrated component (validated)
+
+The account row's location `<select>`, rendered from a Selmer template instead of
+`com/select`. The first interactive modal component off Hiccup; proves the render-file
+path + interop bridge on real, e2e-covered markup (swap 6/6, transaction-edit 8/8).
+
+```clojure
+;; templates/components/location-select.html — plain HTML, {% for %} + {% if selected %}
+(defn location-select* [{:keys [name client-locations value ...]}]
+  (let [options  (cond ...)                        ; [[value label] ...]
+        selected (or value (ffirst options))
+        classes  (str/join " " (conj (vec inputs/default-input-classes) "w-full"))]
+    (sel/render->hiccup "templates/components/location-select.html"
+                        {:name name :classes classes
+                         :options (for [[v l] options] {:value v :label l :selected (= v selected)})})))
+```
+Reuse: pass `inputs/default-input-classes` in (don't hard-code); embed via
+`render->hiccup` so it drops into the still-Hiccup row. See `selmer-conventions.md`.
+
 ## fixed-index row from explicit data — de-faking a deep cursor
 
 When a row always lives at a known index (e.g. simple mode renders exactly `accounts[0]`),