Add shared type definitions and sensitive content redactor

Shared module consumed by both the Express server and the React client:

types.ts:
- ParsedMessage: the normalized message unit (uuid, category, content,
  toolName, toolInput, timestamp, rawIndex) that the parser emits and
  every downstream consumer (viewer, filter, export) operates on
- MessageCategory: 9-value union covering user_message, assistant_text,
  thinking, tool_call, tool_result, system_message, hook_progress,
  file_snapshot, and summary
- SessionEntry / SessionListResponse / SessionDetailResponse / ExportRequest:
  API contract types for the sessions list, session detail, and HTML
  export endpoints
- ALL_CATEGORIES, CATEGORY_LABELS, DEFAULT_HIDDEN_CATEGORIES: constants
  for the filter panel UI and presets (thinking + hook_progress hidden
  by default)

sensitive-redactor.ts:
- 34 regex patterns derived from gitleaks production config, organized
  into Tier 1 (known secret formats: AWS, GitHub, GitLab, OpenAI,
  Anthropic, HuggingFace, Perplexity, Stripe, Slack, SendGrid, Twilio,
  GCP, Azure AD, Heroku, npm, PyPI, Sentry, JWT, PEM private keys,
  generic API key assignments) and Tier 2 (PII/system info: home
  directory paths, connection strings, URLs with credentials, email
  addresses, IPv4 addresses, Bearer tokens, env var secret assignments)
- Keyword pre-filtering: each pattern declares keywords that must appear
  in the text before the expensive regex is evaluated, following the
  gitleaks performance optimization approach
- False-positive allowlists: example/test email domains, localhost/
  documentation IPs (RFC 5737), noreply@anthropic.com
- Pure functions: redactSensitiveContent returns {sanitized, count,
  categories}, redactString returns just the string, redactMessage
  returns a new ParsedMessage with content and toolInput redacted

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

src/shared/types.ts

@@ -0,0 +1,77 @@
+export type MessageCategory =
+  | "user_message"
+  | "assistant_text"
+  | "thinking"
+  | "tool_call"
+  | "tool_result"
+  | "system_message"
+  | "hook_progress"
+  | "file_snapshot"
+  | "summary";
+
+export interface ParsedMessage {
+  uuid: string;
+  category: MessageCategory;
+  content: string;
+  toolName?: string;
+  toolInput?: string;
+  timestamp?: string;
+  rawIndex: number;
+}
+
+export interface SessionEntry {
+  id: string;
+  summary: string;
+  firstPrompt: string;
+  project: string;
+  created: string;
+  modified: string;
+  messageCount: number;
+  path: string;
+}
+
+export interface SessionListResponse {
+  sessions: SessionEntry[];
+}
+
+export interface SessionDetailResponse {
+  id: string;
+  project: string;
+  messages: ParsedMessage[];
+}
+
+export interface ExportRequest {
+  session: SessionDetailResponse;
+  visibleMessageUuids: string[];
+  redactedMessageUuids: string[];
+  autoRedactEnabled?: boolean;
+}
+
+export const ALL_CATEGORIES: MessageCategory[] = [
+  "user_message",
+  "assistant_text",
+  "thinking",
+  "tool_call",
+  "tool_result",
+  "system_message",
+  "hook_progress",
+  "file_snapshot",
+  "summary",
+];
+
+export const CATEGORY_LABELS: Record<MessageCategory, string> = {
+  user_message: "User Messages",
+  assistant_text: "Assistant Text",
+  thinking: "Thinking Blocks",
+  tool_call: "Tool Calls",
+  tool_result: "Tool Results",
+  system_message: "System Messages",
+  hook_progress: "Hook/Progress",
+  file_snapshot: "File Snapshots",
+  summary: "Summaries",
+};
+
+export const DEFAULT_HIDDEN_CATEGORIES: MessageCategory[] = [
+  "thinking",
+  "hook_progress",
+];