test: vendor lich's kiro session-start fixture

[omartelo]

Fixes the `fixtures match lich` CI job, which fails on main since lich registered Kiro CLI as a provider (lichdotdev/lich#442, commit e0aaae1835) and added a `kiro session id` case to `docs/hooks/fixtures/session-start.jsonl`.

What changes

• `tests/fixtures/session-start.jsonl`: refreshed with `tests/refresh-fixtures.sh`, not hand-edited. The only upstream difference across the four fixtures is the new line `{"name":"kiro session id","body":{...,"provider":"kiro"},"accept":{...}}`.
• `tests/hooks.test.mjs`: the pinned provider list in "the vendored fixtures parse..." gains `kiro`. That assertion exists so a new upstream provider is noticed, and it is updated the same way `cursor` was in Report the session title from the turn, not from its end #22. No test is loosened: the enumeration still comes from the fixtures, and every other assertion is unchanged.

Why no hook script changes

• `hooks/report-session-start.sh` does not enumerate providers: it sends `provider=${1:-claude}` from its argument and reads `.conversationId // .session_id` from stdin.
• This plugin does not register Kiro. lich writes its own Kiro agent file (`internal/agentplugin/kiro.go` in lich), which runs this plugin's scripts with `agentSpawn -> hooks/report-session-start.sh kiro`. The Kiro TUI payload carries `session_id`, which the script already reads. lich#442 records an end-to-end run against the v0.12.0 scripts that posted `/session-start {"session_id":...,"provider_session_id":...,"provider":"kiro"}`.
• Cursor CLI is the precedent: a fixture provider with no registration here.

No CHANGELOG entry: nothing a user installs changes.

Test plan

• `tests/refresh-fixtures.sh` leaves only `session-start.jsonl` changed
• `node --test tests/*.test.mjs`: 194 pass, 0 fail (193 pass, 1 fail on the pinned provider list before the test update)
• CI: `hook contract tests` and `fixtures match lich` green