BentoPDF for bau-pm, without third-party hosts (bau-pm BAU-119)

BentoPDF v2.8.8 built from source at its pinned commit with BentoPDF's own
air-gapped build options, every module it would load from a CDN vendored and
checked against vendor.lock, a Content-Security-Policy without a single host,
digital-sign-pdf and timestamp-pdf disabled because both need a third party,
and the hand-off glue on every page: the AGPL source link, the hand-in of a
file from bau-pm through a one-minute cookie into sessionStorage, confirmed by
the tool's reaction, the hand-back of a result from every window, and the
signing tool's flatten switch locked on.

The zero-host gate drives all 117 enabled tool pages in Chromium and fails on
any request to another origin, any CSP violation, a CSP that names a host, and
a disabled id that names no page. Green on this image (3 min 52 s on a private
network), red on the stock upstream image (115 findings) and on a misspelled
id. CI runs it on every push, the release workflow before it pushes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/fixtures/probe.pdf

@@ -0,0 +1,30 @@
+%PDF-1.4
+1 0 obj
+<</Type/Catalog/Pages 2 0 R>>
+endobj
+2 0 obj
+<</Type/Pages/Kids[3 0 R]/Count 1>>
+endobj
+3 0 obj
+<</Type/Page/Parent 2 0 R/MediaBox[0 0 595 842]/Contents 4 0 R/Resources<</Font<</F1 5 0 R>>>>>>
+endobj
+4 0 obj
+<</Length 49>>stream
+BT /F1 24 Tf 72 760 Td (Regierapport Probe) Tj ET
+endstream
+endobj
+5 0 obj
+<</Type/Font/Subtype/Type1/BaseFont/Helvetica>>
+endobj
+xref
+0 6
+0000000000 65535 f 
+0000000009 00000 n 
+0000000054 00000 n 
+0000000105 00000 n 
+0000000217 00000 n 
+0000000313 00000 n 
+trailer<</Size 6/Root 1 0 R>>
+startxref
+376
+%%EOF