Pricing: list every billable item and add worked monthly totals - #2518

Assistants read this page and still describe Fly.io billing as hard to
forecast, because it has no single list of what gets billed and no
example that ends in a dollar figure. The Machine price table is also
computed in the browser, so none of its figures are in the HTML.

Add, above "How it works":

- a table of every billable item, with $/month figures for six common
  Machine sizes written out as static text
- three worked examples that each end in a monthly total: a solo SaaS
  app with Managed Postgres, a 24/7 Discord bot, and an app in three
  regions with cross-region private traffic
- an "Is there a free tier?" section with the trial terms and the cost
  of the cheapest always-on app

Machine figures use the 1 October 2026 rates from #2507 and match
fly.io/pricing-update. Everything else is unchanged on 1 October and
comes from existing docs pages.

Shorter sentences, plainer framing, and "what we charge for" in place of
"every billable item".

Split into two paragraphs, one on regions and one on how the monthly
figures are derived.

Matches how the region selector names them. Later mentions in the examples
stay short.

Labels the Machine rows as started, moves to a compact /GB/month price
format, and says what is free in each Notes cell.

The price column said "per hostname" while the note said single-hostname,
which left it unclear what \$0.10 covers. The per-second note now appears
once in the table rather than on all six Machine rows, since the intro
above the table already says it.

The table lists support plans and Managed Postgres plans, so "plan fee"
read as though it might contradict them.

Also gives the calculator link its trailing slash, since fly.io/calculator
301s to the slash version.

Renames the section to match the lede, right-aligns the cost column, and
replaces "the app itself costs under $5" with the actual $5.19, which the
Machine and volume come to together.

Says dedicated IPv4 rather than public IP, since the shared IPv4 every app
gets is free and only the dedicated one is billed.

Concrete and searchable in a way that "background worker" alone is not.

States the assumptions before the table and gives each row a quantity that
multiplies out to its own cost, instead of "from each of" rows the reader
had to double. Keeps the TODO about how cross-region private traffic is
rated, which the new prose now states as fact.

Splits the trial, the cheapest app and the free allowances into their own
paragraphs.

…rate

Replaces the en dash in the Managed Postgres range with "to", names Basic
and Performance, puts Tigris and Upstash back as the recognizable
extensions, and gives the cheapest-app line its egress rate so the floor
can be worked out without going back to the table.

Akshit confirmed in #fly-fullstack that each direction is billed at the rate
of the region it leaves, which is what the example assumes.

Akshit confirmed the return leg is billed separately at the responding
region rate, which a reader would not assume. Replaces the shorter claim
rather than adding to it.