Add test suite: unit tests for parser, discovery, redactor, exporter, and filters

Comprehensive test coverage for all server services and shared modules:

tests/unit/session-parser.test.ts (16 tests):
- Parses every message type: user (string + array content), assistant
  (text, thinking, tool_use blocks), progress/hook events (from data
  field), file-history-snapshot, summary (from summary field)
- Verifies system metadata (turn_duration) and queue-operation lines
  are silently skipped
- Detects <system-reminder> tags and reclassifies as system_message
- Resilience: skips malformed JSONL lines, returns empty for empty
  files, preserves UUIDs from source
- Integration: parses full sample-session.jsonl fixture verifying all
  9 categories are represented, handles edge-cases.jsonl with corrupt
  lines

tests/unit/session-discovery.test.ts (6 tests):
- Discovers sessions from {version, entries} index format
- Handles legacy raw array format
- Gracefully returns empty for missing directories and corrupt JSON
- Aggregates across multiple project directories
- Uses fullPath from index entries when available

tests/unit/sensitive-redactor.test.ts (40+ tests):
- Tier 1 secrets: AWS access keys (AKIA/ASIA), Bedrock keys, GitHub
  PATs (ghp_, github_pat_, ghu_, ghs_), GitLab (glpat-, glrt-),
  OpenAI (sk-proj-, legacy sk-), Anthropic (api03, admin01),
  HuggingFace, Perplexity, Stripe (sk_live/test/prod, rk_*), Slack
  (bot token, webhook URL), SendGrid, GCP, Heroku, npm, PyPI, Sentry,
  JWT, PEM private keys (RSA + generic), generic API key assignments
- Tier 2 PII: home directory paths (Linux/macOS/Windows), connection
  strings (PostgreSQL/MongoDB/Redis), URLs with embedded credentials,
  email addresses, IPv4 addresses, Bearer tokens, env var secrets
- False positive resistance: normal code, markdown, short strings,
  non-home file paths, version numbers
- Allowlists: example.com/test.com emails, noreply@anthropic.com,
  127.0.0.1, 0.0.0.0, RFC 5737 documentation IPs
- Edge cases: empty strings, multiple secrets, category tracking
- redactMessage: preserves uuid/category/timestamp, redacts content
  and toolInput, leaves toolName unchanged, doesn't mutate original

tests/unit/html-exporter.test.ts (8 tests):
- Valid DOCTYPE HTML output with no external URL references
- Includes visible messages, excludes filtered and redacted ones
- Inserts redacted dividers at correct positions
- Renders markdown to HTML with syntax highlighting CSS
- Includes session metadata header

tests/unit/filters.test.ts (12 tests):
- Category filtering: include/exclude by enabled set
- Default state: thinking and hook_progress hidden
- All-on/all-off edge cases
- Redacted UUID exclusion
- Search match counting with empty query edge case
- Preset validation (conversation, debug)
- Category count computation with and without redactions

src/client/components/SessionList.test.tsx (7 tests):
- Two-phase navigation: project list → session list → back
- Auto-select project when selectedId matches
- Loading and empty states
- onSelect callback on session click

tests/fixtures/:
- sample-session.jsonl: representative session with all message types
- edge-cases.jsonl: corrupt lines interspersed with valid messages
- sessions-index.json: sample index file for discovery tests

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

tests/fixtures/sessions-index.json

@@ -0,0 +1,23 @@
+{
+  "version": 1,
+  "entries": [
+    {
+      "sessionId": "test-session-001",
+      "fullPath": "/tmp/test-session-001.jsonl",
+      "summary": "Fix authentication bug in login flow",
+      "firstPrompt": "Can you help me fix the login bug?",
+      "created": "2025-10-15T10:30:00Z",
+      "modified": "2025-10-15T11:45:00Z",
+      "messageCount": 12
+    },
+    {
+      "sessionId": "test-session-002",
+      "fullPath": "/tmp/test-session-002.jsonl",
+      "summary": "Add dark mode support",
+      "firstPrompt": "I want to add dark mode to the app",
+      "created": "2025-10-16T14:00:00Z",
+      "modified": "2025-10-16T15:30:00Z",
+      "messageCount": 8
+    }
+  ]
+}