fix(security): widget consents and shared files cleared on logout; forged shares refused (#266, #267)

#266: remembered widget approvals (lotus.widgetConsent.*) survived logout,
so they applied silently to the next account on the device and listed the
previous account's rooms; clearPlaintextCaches now sweeps them. Space
structure, call membership and Lotus room-policy state join
PROTECTED_STATE_TYPES, so no widget can be granted them.

#267: any website could auto-submit a form to /share-target and land the
user in the share picker with attacker-chosen text and files. The worker
now refuses a share whose Origin is another site. (Sec-Fetch-Site, as the
issue suggested, never reaches a service worker: checked in Chromium.)
Origin null/absent, as the OS share sheet sends, stays accepted, and
/share now says the content came from another app or website. Both logout
paths await clearSharedPayload(); the server-forced one also clears the
soundboard clip cache, as #57 intended.

Fixes #266
Fixes #267

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/pages/client/share/Share.tsx

@@ -145,6 +145,11 @@ export function Share() {
               <Box direction="Column" gap="400">
                 <Box direction="Column" gap="200">
                   <Text size="L400">Shared</Text>
+                  {/* [Gitea #267] Not everything that arrives here came from the
+                      user's share sheet; say so before they pick a room. */}
+                  <Text size="T200" priority="300">
+                    This came from another app or website. Check it before you send it.
+                  </Text>
                   {shared.files.map((f) => (
                     <Box key={f.name} alignItems="Center" gap="200">
                       <Icon