v0.5.0 — daylight, and a city that survives a slow machine

Daylight arrives, and the city stops going dark on ordinary hardware.

Fixed

• The city no longer goes black when the frame rate drops. A user sent two
  screenshots side by side: a vivid city at medium quality, and near-black
  silhouettes on the same build. The night theme's whole visual language rides
  on the bloom pass — structure is matte, meaning is neon, and only emissive
  above 1.0 crosses the threshold — so turning bloom off did not dim the city,
  it stopped it communicating. And it was automatic, which meant the people who
  saw it were those on the weakest hardware. Bloom is now the last thing
  dropped: a new reduced tier turns down pixel ratio, particles, labels and
  antialiasing while keeping the lighting, and measures about 40% faster than
  medium. Below that, neon repaints as saturated base colour with a minimum
  luminance, so a dirty page still reads as dirty.
• The quality downgrade no longer fires on a boot stall. Three seconds
  ignored, a four-second settle, then three sustained seconds under the floor.
  The notice now names what was lost and offers one click to undo it.
• Labels no longer draw through solid buildings. They are DOM elements
  positioned by CSS2DRenderer, so they never took part in depth testing; a
  label behind a tower had always drawn over it. They are now occluded by
  raycasting against the collision structure the walker already maintains,
  amortised across frames and faded rather than snapped.
• $PGDATA is gone from the user-facing text. It names an environment
  variable, and in a configuration where it points at a config-only directory
  the data lives elsewhere. The excavation is the data directory. A test
  holds the line — and immediately caught a regression that a later merge
  reintroduced.

Added

• A daylight theme for the city, not just the panels. Day mode used to stop
  at the edge of the UI: paper panels over a city still lit for night. It is now
  a sunlit model in the spirit of SimCity — flat saturated colour with a hard
  split between the lit and shaded faces of every mass, a warm directional sun
  casting real shadows from 172 architectural casters (about 4% of frame time,
  with the buffer field excluded because its heights change every frame), light
  ground the city sits on top of, and districts wearing their semantic colours
  as zones so the layout can be read from altitude before a single label.
  Night's rule is structure matte, meaning neon; day's is structure sunlit,
  meaning saturated. The colours keep their meanings exactly.
• A visible theme switcher. Daylight was toggled by pressing N and by
  nothing else — undiscoverable on a desktop and unreachable on a phone.
• Google Maps mouse convention. Left-drag pans, shift-left-drag rotates and
  tilts, and right-click is freed for a context menu that offers what the
  thing under the cursor actually supports — including opening the page anatomy
  view directly from a heap file or an index, which is a better home for it than
  any panel. Touch is unchanged.
• CLAUDE.md, AGENTS.md and CONTRIBUTING.md. Every rule carries the
  reason it exists, because a rule without one gets dropped the first time it is
  inconvenient. Red/green TDD is mandatory and CI fails the build on a red test.

Known issues

• Cache hit ratio settles near 87% where a healthy production system sits at
  98–99%.
• The touch controls have been verified only in Chrome's mobile emulation, which
  differs from iOS Safari in touch handling and viewport units.