CSP tripwire: source-scan test + AGENTS.md rule; drop last native onchange

templates/csp_source_test.go scans .templ sources and fails the build on
the three authoring patterns hash-mode CSP refuses silently: native on*=
handler attributes (quote and templ brace forms), inline <script>
content outside the sanctioned theme_flash_guard.templ, and htmx's
eval-dependent bindings (hx-on*, js:-prefixed hx-vals — 'unsafe-eval' is
not granted). Verified to fire on all four violation classes via a
scratch probe file.

The dry run immediately caught a live leftover: unlinked_books.templ's
onchange="updateSelectedCount()" — CSP-refused since the hash flip.
Removed; the count already updates through the document-level delegated
change listener that x-init="setupEventDelegation()" registers.

AGENTS.md gains a "CSP discipline" ALWAYS-apply section documenting the
hash allow-list, the sanctioned-guard invariant, the replacement
patterns, and the tripwire test.

Verified: go build/vet, templates+middleware+docs tests green; /unlinked-
books loads with zero console violations (no fixture rows to exercise the
checkbox; the delegated path is unchanged code).

templates/unlinked_books.templ

@@ -108,7 +108,7 @@ templ UnlinkedBooks(user User, unlinkedBooks []UnlinkedBookData) {
 						<div class="card p-6">
 							<div class="flex gap-6">
 								<div class="flex items-start pt-2">
-									<input type="checkbox" class="unlinked-checkbox w-5 h-5" data-progress-id={ book.ProgressID } data-title={ book.TitleFromDevice } onchange="updateSelectedCount()"/>
+									<input type="checkbox" class="unlinked-checkbox w-5 h-5" data-progress-id={ book.ProgressID } data-title={ book.TitleFromDevice }/>
 								</div>
 								<div class="flex-1 min-w-0">
 									<div class="flex items-center gap-3 mb-4">