Fix crash on reports with a null timezone in GET /reports/:id

[ZIJ]

Cause: handleRequest in app/api.mjs called report.timezone.trim() unconditionally. Legacy report records (created before timezone tracking existed) have timezone: null, so this threw "TypeError: Cannot read properties of null (reading 'trim')" and the request returned 500, matching the captured Sentry event for GET /reports/report-legacy.

Fix: default a missing/null timezone to "UTC" before trimming: (report.timezone ?? "UTC").trim(). Reports with a valid timezone string are unaffected; reports with a null timezone now render using UTC instead of crashing.

Regression test: app/test/api.regression.test.mjs exercises handleRequest with a synthetic report derived from the incident's captured state (id "report-legacy", timezone: null) and asserts a 200 response with a non-empty fallback timezone and generatedAt string, instead of the request throwing.

Sentry incident: event. This is the deliberately faulty on-call example app.

Tested against commit b664e075ca7c0173b06f344d47a8cbcfa6e426fa. The same regression command failed before the fix and passed afterward:

node --test --test-reporter=tap --test-concurrency=1 app/test/api.regression.test.mjs app/test/api.test.mjs app/test/worker.test.mjs
Exit 1
TAP version 13
# Subtest: GET report with a null timezone falls back to a default instead of crashing
not ok 1 - GET report with a null timezone falls back to a default instead of crashing
  ---
  duration_ms: 58.641637
  type: 'test'
  location: '<verification>/before/app/test/api.regression.test.mjs:19:1'
  failureType: 'testCodeFailure'
  error: "Cannot read properties of null (reading 'trim')"
  code: 'ERR_TEST_FAILURE'
  name: 'TypeError'
  stack: |-
    handleRequest (file://<verification>/before/app/api.mjs:9:36)
    TestContext.<anonymous> (file://<verification>/before/app/test/api.regression.test.mjs:20:26)
    Test.runInAsyncScope (node:async_hooks:214:14)
    Test.run (node:internal/test_runner/test:1047:25)
    Test.start (node:internal/test_runner/test:944:17)
    startSubtestAfterBootstrap (node:internal/test_runner/harness:296:17)
  ...
# Subtest: GET returns a report with its timestamp in the configured timezone
ok 2 - GET returns a report with its timestamp in the configured timezone
  ---
  duration_ms: 84.714596
  type: 'test'
  ...
# Subtest: unknown reports and unmatched routes return 404
ok 3 - unknown reports and unmatched routes return 404
  ---
  duration_ms: 1.425469
  type: 'test'
  ...
# Subtest: report writes are rejected
ok 4 - report writes are rejected
  ---
  duration_ms: 0.95472
  type: 'test'
  ...
# Subtest: a bounded batch processes healthy jobs in creation order
ok 5 - a bounded batch processes healthy jobs in creation order
  ---
  duration_ms: 16.077736
  type: 'test'
  ...
# Subtest: CSV output preserves commas, quotes, and embedded newlines
ok 6 - CSV output preserves commas, quotes, and embedded newlines
  ---
  duration_ms: 0.327159
  type: 'test'
  ...
# Subtest: completed jobs are not repeated when another batch runs
ok 7 - completed jobs are not repeated when another batch runs
  ---
  duration_ms: 0.509935
  type: 'test'
  ...
1..7
# tests 7
# suites 0
# pass 6
# fail 1
# cancelled 0
# skipped 0
# todo 0
# duration_ms 679.448554

node --test --test-reporter=tap --test-concurrency=1 app/test/api.regression.test.mjs app/test/api.test.mjs app/test/worker.test.mjs
Exit 0
TAP version 13
# Subtest: GET report with a null timezone falls back to a default instead of crashing
ok 1 - GET report with a null timezone falls back to a default instead of crashing
  ---
  duration_ms: 83.293418
  type: 'test'
  ...
# Subtest: GET returns a report with its timestamp in the configured timezone
ok 2 - GET returns a report with its timestamp in the configured timezone
  ---
  duration_ms: 83.624762
  type: 'test'
  ...
# Subtest: unknown reports and unmatched routes return 404
ok 3 - unknown reports and unmatched routes return 404
  ---
  duration_ms: 1.402416
  type: 'test'
  ...
# Subtest: report writes are rejected
ok 4 - report writes are rejected
  ---
  duration_ms: 0.932459
  type: 'test'
  ...
# Subtest: a bounded batch processes healthy jobs in creation order
ok 5 - a bounded batch processes healthy jobs in creation order
  ---
  duration_ms: 16.196487
  type: 'test'
  ...
# Subtest: CSV output preserves commas, quotes, and embedded newlines
ok 6 - CSV output preserves commas, quotes, and embedded newlines
  ---
  duration_ms: 0.332082
  type: 'test'
  ...
# Subtest: completed jobs are not repeated when another batch runs
ok 7 - completed jobs are not repeated when another batch runs
  ---
  duration_ms: 0.515313
  type: 'test'
  ...
1..7
# tests 7
# suites 0
# pass 7
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 700.819616