Make the graph page read correctly

[WaylandYang]

Thirty-odd rounds of looking at the graph page and fixing what did not read.
Frontend only, except two small backend additions noted below.

Derived edges

• The toggle moved out of the class legend into the bottom-left tower. It looked
  like a tenth class there, and the fix could not be colour: this file's own rule
  is chrome carries no hue, colour belongs to data. So it moved instead.
• Derived edges fade in after the asserted ones, on load and on toggle.
  Order is the content: what people wrote lands first, what the engine worked out
  arrives second.
• Two richer attempts were tried and dropped — see "What we tried and rejected".
• The selected/hovered state keeps a derived edge gold instead of turning it
  white. Selection is when you look closest; that is the worst moment to erase
  where an edge came from.
• Inference panel: opens in place from its button (the shared FLIP popover, same
  as notifications and the user menu), and "Run now" asks first — on a second
  button, because two clicks on one control already means "close" here.

Class legend

• Capped at 6 pills, ordered by how many nodes each class actually has. The rest
  collapse into "All N classes", which opens a searchable list of every class
  with per-class counts.
• Each row has "Only"; a "Show all (N hidden)" chip appears whenever anything is
  hidden, so filtering is never silent.

Timeline

• A step unit (year / month / day) that drives both playback and the histogram
  buckets. Before this the bars were years while playback stepped by days, and
  nothing on screen said how long one step was.
• Playback advances continuously instead of jumping bucket to bucket; scrubbing
  seeks instead of stopping; bars ahead of the playhead are no longer lit; the
  track glows once when a run finishes.
• Bar width scales with the unit — fat blocks for years, hairlines for days.

Routing

• The knowledge base is now a path segment: /kb/$kbId/... for graph, search,
  chat, library, ontology, mappings, review and settings. Old paths still work
  and redirect. A link that omits the base used to silently show the reader
  their base — same screen, different data.
• The graph page writes entity, focus and at into the URL, so a link
  reproduces what you are looking at, including the moment in time.
• A no-access / missing base lands on a real page instead of an empty graph.

Correctness

• Timezone. World time (valid_from/valid_to) is a calendar date from a
  document and renders in UTC everywhere; belief time (recorded_at) is a real
  instant and renders in the reader's zone. Entity history was doing the former
  to the latter, shifting revisions by a day for anyone east of UTC. The two
  functions now sit side by side with comments saying they are deliberately
  different.
• Popover surfaces had a blue cast (rgba(14,14,16)), which reached the
  notification card, the user menu and both new panels. Now neutral.
• Panels grow more opaque on pointer-enter and while playback runs — glass is
  for when you are not reading it.
• Facts count in the top-right now reads "N of M" like the entity count did;
  the two idioms in one sentence made it look broken when the budget changed.
• An entity count control (150 / 300 / 600 / 1000) next to those stats, with a
  limit parameter on the overview endpoint (clamped server-side).

Bugs fixed along the way

• Finishing playback twice reloaded the page: an onAnimationEnd handler was
  calling .remove() on a React-owned node, so the next keyed render threw
  NotFoundError and unmounted the tree.
• Hovering brightened edges and nodes that do not exist at the current instant —
  the hover branches returned before the time filter.
• Turning derived off with a node selected flashed unrelated edges: the fade-out
  started from full gold instead of from the colour they already had.
• A dense histogram rendered empty: a fixed 2px gap consumed the whole track at
  214 bars.
• A transition shorthand on .glass-strong silently dropped the island's width
  transition, because unlayered CSS beats a Tailwind utility.

What we tried and rejected

• Animating the derivation (premises lighting in order, then the conclusion).
  Two versions, neither readable: with hundreds of edges on screen you cannot
  tell which premises belong to which conclusion. The entity sidebar's Derived
  tab already says it one row at a time. The backend field added for it was
  reverted rather than left unread.
• Scaling the ForceAtlas2 constants with graph size. It spread better and
  felt limp; the deliberately strong values are back.
• A Morandi palette — rejected earlier, noted here because the comment
  explaining why now sits in palette.rs.

Backend

Two additions only: limit on graph/overview, and nothing else that ships —
the derived-premise field was added and then reverted with the animation.

Notes

Verified against the demo base (548 entities / 912 facts / 28 derived edges).
Animation timing could not be observed in the preview environment, which does
not advance CSS transitions or requestAnimationFrame; end states and layout
were measured instead, and that limitation is called out where it matters.

🤖 Generated with Claude Code