feat: decouple manual image sharing from automation gating

The "Share a saved image" panel was wired to the automated exchange
engine, so an operator could only share an image right after an inbound
image request, limited to assets the auto-exchanger would itself pick.

Add a manual path that offers any enabled, unused library image at any
point (no request detection, tier, seller, or boundary gating) and sends
it with no reciprocal "your turn" text. Safety flags now surface as a
non-blocking warning instead of disabling the panel. The automated
auto-send path keeps all its guardrails; the shared image-delivery step
is extracted into a helper used by both paths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/api-contracts/src/chats.ts

@@ -93,9 +93,13 @@ export const SuggestedReplyResponseSchema = z.strictObject({
 });
 export const SendReplyRequestSchema = z.strictObject({ message: z.string().min(1) });
 export const ConversationMediaShareOptionsResponseSchema = z.strictObject({
+  /** What the latest inbound message asked for, if anything. Informational only — never gates sharing. */
   requestKind: z.union([MediaLibraryTagSchema, z.literal('generic')]).nullable(),
   assets: z.array(MediaLibraryAssetSchema),
+  /** Set only when there is genuinely nothing to share (no room, or no enabled/unused images). */
   reason: z.string().nullable(),
+  /** Non-blocking safety note (seller/boundary flags). The operator can still share. */
+  warning: z.string().nullable(),
 });
 export const ShareConversationMediaRequestSchema = z.strictObject({ assetId: z.string().uuid() });
 export const StartConversationRequestSchema = z.strictObject({