feat(broadcasts): list filters, account-wide stats, and link clicks

[imjohnbo]

Part 4 of 8. Base: #16.

What this adds

List filters:

kit broadcasts list --status <draft|scheduled|sending|completed|aborted>
kit broadcasts list --sent-after <yyyy-mm-dd> --sent-before <yyyy-mm-dd>

Account-wide stats. The stats subcommand now takes an optional ID:

kit broadcasts stats 12     # GET /v4/broadcasts/12/stats, as before
kit broadcasts stats        # GET /v4/broadcasts/stats, one row per broadcast

Without an ID it accepts --status, --sent-after, --sent-before, --include-total-count, and the pagination flags.

Link clicks:

kit broadcasts clicks <id>

Design notes

Single-broadcast stats output gains unsubscribe_rate, progress, and the two tracking flags. The spec documents all four. The CLI dropped them.

Tracking prints as enabled or disabled instead of as the raw *_disabled booleans. The JSON shape does not change, so existing scripts keep working. A test covers this.

broadcasts create now parses --tag-ids and --segment-ids with parseIdList from part 1.

Review notes

One subcommand covers both stats endpoints. An optional argument reads better than a second subcommand, and it keeps kit broadcasts stats <id> working exactly as before.

Tests: 232 before, 264 after.

Closes #4
Closes #7
Closes #11
Part of #13

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The stack

Merge from the top down. Each part builds on the one above it.

	PR	Contents
1	#14	Client query support and shared helpers
2	#15	Sequence CRUD and sequence emails
3	#16	Posts and snippets
4	#17 (this one)	Broadcast filters, account-wide stats, link clicks
5	#18	Subscriber slim listing, warnings, filter
6	#19	Tag rename, remove-by-email, bulk delete
7	#20	Account endpoints and purchase create
8	#21	Spec coverage map and its tests

Base branch: main for part 1, the previous part's branch for the rest.
GitHub retargets each base to main as the part below it merges.