feat(analytics): analytics page, and dashboard money from the API

[PhilippTheServer]

Closes #7 · consumes OpenTaberna/fastapi#44

The dashboard summed revenue and AOV client-side from the last 100 orders — its own comment
said so. Those figures now come from /v1/admin/analytics/*, computed in SQL over the whole
order history, and a new Analytics page adds the trend, product and funnel views that
did not exist.

What's here

Analytics page — net revenue over time, orders and units, the order funnel with drop-off
per step, per-SKU performance with return rate, and active-but-unsold stock. Period selector
of 7 / 30 / 90 days / 12 months, switching to weekly buckets past 120 days because daily
buckets over a year are unreadable.

Dashboard — money tiles read the summary endpoint over 30 days. Work queues still read
the orders list, which is correct for them: "what needs doing now" is the newest orders.

Decisions worth reviewing

No Angular chart wrapper. Chart.js is used directly behind a thin standalone component.
The app is zoneless and on Angular 22, and a wrapper's peer range gates every future Angular
upgrade — ng2-charts@10 would also pull in @angular/cdk, which this app does not
otherwise use. Only the controllers actually drawn are registered, so the rest of Chart.js
tree-shakes away.

Chart.js is not in the initial bundle. It sits in a lazy chunk (187 kB raw / 57 kB
transfer) loaded only by /analytics. Initial total is unchanged at 345.94 kB / 93.41 kB.

While wiring this I caught a real problem: the dashboard imported rangeEndingToday from
analytics.page.ts, which drags the analytics page — and through it Chart.js — into the
dependency graph of a screen that draws no charts. The helpers moved to core/date-range.
grep -rln "from 'chart.js'" now returns only the two chart components and the analytics
page.

Currencies are never summed. The API returns a list keyed by currency; the page renders
one block each and charts the highest-earning one, saying so when there is more than one.

No baseline renders as "no prior data". Change from zero is undefined — not 0%, and not
an arrow.

Verification

$ npx ng test --watch=false
 Test Files  9 passed (9)
      Tests  53 passed (53)

$ npx prettier --check "src/app/**/*.{ts,html}"
All matched files use Prettier code style!

$ npx ng build
Application bundle generation complete.
Initial total | 345.94 kB | 93.41 kB

The dashboard specs catch the actual regression. Restoring the client-side sum — with an
orders stub carrying a 999999 order that would dominate any such sum:

 × reports net revenue from the API, not from the orders list
 × shows the currency that earned the most, never a sum across them
 × degrades to zero and flags a partial view when analytics fails
AssertionError: expected 999999 to be 40000 // Object.is equality

The analytics page spec is a render test with teeth: it compiles the template, runs every
computed and builds real Chart.js configurations, so a mistyped field fails in CI rather
than on an operator's screen.

nav.model.spec.ts was updated from six navigation entries to seven — an intentional change
to an existing assertion, not a loosened one.

Verified against the live dev stack: all four endpoints answer, and 403 without a token.