feat: deliver the fork delta since the 1108 sync wave - #836

What this changes

Delivers the fork delta accumulated since the 1108 sync wave as one batch commit on top of
master (the single-batch delivery the fork sync policy prescribes). Nothing here changes the
recorded contracts; it is feature, fix, test and harness work that master predates.

• Screenshot-view: a fitted PNG render of a store head, from the CLI (view-screenshot with its
  help, session and export plumbing) and from the window (apps/beamcraft-ui/src/screenshot.rs
  with its suite): the camera fits the framed elements, the catalogue colours apply to the
  render, and the background is a light paper tone instead of the renderer's dark clear colour
  so a frame can match a drawing-style reference picture.
• Catalogue colouring by element class in the viewport (issue 526): the owner palette decision
  (member/plate/bolt hues, recorded 2026-11-06) rides as an automatic default set the window
  evaluates read-only in the background, colour sets are selectable in the window and persist,
  and the colour-filter class document describes the evaluation.
• Bolt groups: the grip length is decided from the actual crossed faces instead of the parts'
  conservative boxes — face-exact under any placement rotation, merged overlapping parts, a
  part without a usable mesh grips per its box which errs long and never under (issue 519
  defect B); the bench form previews the bolt row and its holes before commit (V19 slice 3);
  the engine, command and viewport layers carry the decision with tests.
• The sample library's M20 bolts drop the 160 mm length again: this reverts the one
  sample-library line carried by feat: deliver the fork delta since the 1106 sync wave #834, on the fork's acceptance rehearsal decision — the
  length list returns to 55–150.
• Release packages ship the fastener and section libraries of assets/libraries/ beside the
  Inter font and the project documents (Q02 rehearsal); the packaging document paragraph says
  so.
• Q01 stories: the section-about-the-axis placement gets its own expanded-scenario story (P14).

Fork-only policy (its workflow forms, docs/plan/, visual evidence, fork tooling) is not part
of this delivery; the upstream-owned Python CI tools are untouched. Bare issue NNN references
carry the fork tracker's numbers, as in the previous delta waves.

How you verified it

• cargo fmt --all -- --check (recorded gate stage, exit 0)
• cargo clippy --workspace --all-targets -- -D warnings (recorded gate stage, exit 0)
• cargo test --workspace (recorded gate: 2665/2665 runnable tests executed with nextest
  0.9.149 on macOS aarch64, plus mandatory doctests and cargo doc -D warnings, all exit 0;
  the committed fork master merge equals the tested tree, receipt bound in the merge
  commit)
• This batch differs from that merge tree only by the fork-only policy paths named above,
  which carry no Rust code; upstream CI gates the delivered tree.

Never-crash

Every model file, IFC/DSTV import and keystroke is untrusted input (AGENTS.md §4).

• No new unwrap/expect/panic!/todo! outside tests
• No indexing or slicing with input-derived positions; allocations sized by input are capped
• No unsafe

Provenance

Read AGENTS.md §1 and §2 before adding any asset.

• Nothing taken from Tekla Structures or any Trimble product (assets, code, documentation, tables)
• No GPL/AGPL code copied in
• No new assets (the DIN fastener library change removes one length from the existing
  contributor-original synthetic library entry)

Anything a reviewer should look at first

• The assets/libraries/din-fasteners.usda one-line revert of feat: deliver the fork delta since the 1106 sync wave #834's 160 mm M20 length: the
  fork's acceptance rehearsal removed it after this delivery branch was cut, so the batch
  carries the revert; the viewport fastener-stack test pins the remaining lengths.
• The two Windows-path test failures reported in feat: deliver the fork delta since the 1106 sync wave #834's review note live in files this delta
  does not touch; they ride a separate fix.

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