Three per-request costs removed from the eval path:

- the full EngineState clone (existed only to attach a per-request
  ThreadJob; the engine now carries one long-lived background job,
  attached at construction, shared by all evals)
- the jobs-table add/remove and its global mutex
- the OS thread spawn (a fixed pool sized to core count evaluates
  requests; streaming responses hand their drain loop -- including the
  first-value peek, which can block on follow-style handlers -- to a
  spawned thread so they never pin a worker; when every worker is busy
  the pool falls back to thread-per-request, so it cannot starve)

bench --bench throughput, hello-world: 61.9us -> 15.4us/req sequential
(16.2K -> 65.1K req/s); 16-in-flight 41.1K -> 531K req/s.

… base

…wsers

…ings

…rose for article

… literal

Drop the hand-mixed --panel/--on-dim/--line color-mix tints for stellar ramp
tokens, following the reference pattern (surface step / -on / -dim). --panel
becomes a .panel utility on the +1 step; cards compose 'card panel'.

Source Code Pro's subset lacked box-drawing glyphs, so Nushell table output
fell back to a different-width font and columns drifted. Iosevka X (custom
no-ligature build, dotted zero, regular+bold, subset to ~42KB/weight) ships
them, so tables and ASCII line up. Recipe vendored as iosevka-x.build-plan.toml;
--font-mono retuned in stellar.config.json and stellar.css regenerated.

…corners

Move block code from the secondary --code-inner-bg to stellar's primary
--code-bg (the surface its syntax palette is tuned for), reseeded to a cool
hue via colors.code.index=4 so it harmonizes with the blue (aqua in light,
deep teal in dark) - and makes the index a real knob. Inline <code> keeps
--code-inner-bg, with an em-relative 0.2em radius (was an oversized ~8px).

…bles/lists; low-asterisk font

- code line-height -> 1.2 (--code-line-height var) so box-drawing tables join;
  scrollbar-gutter:stable instead of fat line-height for the overflow scrollbar
- inline code: em padding + small radius (justified literals; size/radius
  scales floor too high for an inline chip)
- table cells + link underline + list line-height tightened
- re-vendored Iosevka X with the low (penta-low) asterisk + crossing eight
- mint --border-radius--1/--2 (radii.negativeSteps=2)

…ocked)

…to two levels

…llar ramps

…ign/button

…t mode)

…living example

…e to avoid 2048 collision

…r-scheme); drop duplicate button:hover