Get a weekly Bitly traffic digest without partial week errors

**Objective:** Write a digest of the last `{weeks}` weeks of clicks (default 4) for `{group-name}` (default: all groups), comparing the latest complete week with the ones before it.

**Step 1: Weekly clicks**

Call `bitly-get-click-week` with `week-starting-date.from` = the start of the week `{weeks}` weeks ago, `week-starting-date.to` = the start of the current week, and `group-name` when given. Raise `max-records` until the full set is returned. Treat the current, partial week separately and say so.

**Step 2: Compare**

* Total clicks per week, and the change of the last complete week against the average of the weeks before it.
* Per `link`: the last complete week vs the prior average. Rising = up at least 50% with at least 20 clicks; falling = down at least 50% from at least 20 clicks.

**Step 3: New links**

Call `bitly-get-bitlink` with `created-date.from` = the start of the window and `group-name` when given. For each, report its clicks so far from Step 1.

**Step 4: Report**

* Headline: total clicks last complete week and the percentage change
* A small table of weekly totals
* Top 5 links last week
* Rising links and falling links (link, title, last week, prior average)
* New links created in the window and how they are doing
* One or two sentences on what changed

**Rules & Guidelines:**

* Do not call `bitly-add-bitlink` or `bitly-update-bitlink`. This prompt is read-only.
* Use whole weeks as Bitly reports them by `week-starting-date`; do not rebuild weeks from daily data.

**Validation:**

* If there are no clicks in the window, say so and stop.
* If `{weeks}` is less than 2, use 2, since a digest needs a comparison.