v0.10.0 — real PostgreSQL, and a map instead of a pipeline

Real PostgreSQL behind the query surface, and a 2D view that draws the
architecture rather than a row of boxes.

Added

• Real PostgreSQL, opt-in. A running server exposes catalogs, pg_stat_*
  counters, EXPLAIN and log output — and nothing else. Not the clock sweep
  choosing a victim frame, not a page landing in a specific buffer, not the
  checkpointer's write phase. Those are exactly what this project draws, so
  neither source alone is enough. PGlite now supplies what only it can: real
  parsing, so a typo produces a genuine PostgreSQL error; the real plan,
  with true node types, costs, estimates against actuals and real buffer
  counters; real catalogs; real results. The model keeps supplying the interior.
  They meet at the plan — the real one drives the animation. It is lazy and
  opt-in, so the city's bundle is unchanged, and which numbers are real and
  which are modelled is visible at a glance, because that distinction is the
  entire reason for adding it.
• The 2D view draws architecture now. The first version was a pipeline: a
  line of stops with the current one lit, which communicates order and nothing
  else. Following the conventions of Momjian's internals diagrams and Lesovsky's
  observability map, it now has containment — one shared segment visibly holding
  the buffer pool, wal_buffers, the ProcArray and the lock table, with private
  backend memory visibly outside it — connections with direction, layers where
  the axis means something, and the query path animating across the structure
  rather than replacing it.

Fixed

• Analytics were never being received. The deployed integration was
  Plausible's older form while the account issues the current one, where the site
  identity is embedded in the script filename. The script was serving correctly
  and the account was looking for something else.
• The controls table had been wrong for three releases. It said right-drag
  orbits; right-drag was freed for the context menu in v0.6.0 and rotation is
  shift with left-drag. Someone asked how to rotate the camera on Hacker News,
  and this table is what they would have found.
• Overlays no longer print on top of the inspector on a phone. Two elements
  shared a z-index with the drawer, so paint order was decided by document order
  rather than intent. z-index is a named scale now.

Removed

• Plausible dashboard setup steps from the README. That is a one-time task for
  one person's account, not documentation, and it is GitHub issue #3 now.