feat: implement Inbox view with triage actions

- Add InboxItem types and TriageAction/DeferDuration types
- Create Inbox component with:
  - Accept/Defer/Archive actions for each item
  - Keyboard shortcuts (A/D/X) for fast triage
  - Defer duration picker popup
  - Inbox Zero celebration state
  - Type-specific badges with colors
- Add comprehensive tests for all functionality

Closes bd-qvc

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/types.ts

@@ -118,6 +118,39 @@ export interface DecisionEntry {
 /** Staleness level derived from item age */
 export type Staleness = "fresh" | "normal" | "amber" | "urgent";
 
+// -- Inbox types --
+
+/** Type of work item in the inbox */
+export type InboxItemType = "mention" | "mr_feedback" | "review_request" | "assignment" | "manual";
+
+/** A work item awaiting triage in the inbox */
+export interface InboxItem {
+  /** Unique identifier */
+  id: string;
+  /** Human-readable title */
+  title: string;
+  /** Type of inbox item */
+  type: InboxItemType;
+  /** Whether this item has been triaged */
+  triaged: boolean;
+  /** When the item was created/arrived */
+  createdAt: string;
+  /** Optional snippet/preview */
+  snippet?: string;
+  /** Source project */
+  project?: string;
+  /** Web URL for opening in browser */
+  url?: string;
+  /** Who triggered this item (e.g., commenter name) */
+  actor?: string;
+}
+
+/** Triage action the user can take on an inbox item */
+export type TriageAction = "accept" | "defer" | "archive";
+
+/** Duration options for deferring an item */
+export type DeferDuration = "1h" | "3h" | "tomorrow" | "next_week";
+
 /** Compute staleness from an ISO timestamp */
 export function computeStaleness(updatedAt: string | null): Staleness {
   if (!updatedAt) return "normal";