feat(skills): add html-artifact skill, fold in sketch + architecture-diagram + concept-diagrams (#48899)

* feat(skills): add html-artifact skill, fold in sketch + architecture-diagram + concept-diagrams

Adds a unified `html-artifact` creative skill that produces self-contained,
single-file HTML artifacts — concept explainers, implementation plans,
status/incident reports, code-review walkthroughs, technical + educational
SVG diagrams, multi-variant design comparisons, and throwaway editors that
export their state back to the clipboard. Grounded in Anthropic's
html-effectiveness gallery (MIT); the house style (token block, serif/sans/
mono split, hand-rolled diffs, inline-SVG diagrams, graceful degradation) is
distilled from reading all 20 reference files.

Supersedes and removes three overlapping skills, folding their unique value in:
- sketch              -> the fidelity dial (throwaway vs presentation) + the
                         multi-variant comparison layouts + the browser-vision
                         verify loop (references/fidelity-and-verify.md)
- architecture-diagram-> the dark "infra" token variant + double-rect masking +
                         semantic component palette (references/dark-tech.md,
                         templates/diagram.html infra mode)
- concept-diagrams    -> the 9-ramp educational color system + the concept
                         archetype library (references/concept-archetypes.md,
                         the light design system in templates/diagram.html)

Structure:
- SKILL.md (description exactly 60 chars), 6 references, 3 templates
- templates verified by headless-Chrome render + vision inspection
- editor export logic (file://-safe clipboard, Promise-normalized) verified in node

Cross-references updated in claude-design (new disambiguation table row drawing
the design-taste vs information-artifact boundary), design-md, pretext, spike,
and kanban-video-orchestrator. Website skill docs + catalogs regenerated;
stale EN/zh-Hans per-skill pages pruned and i18n cross-refs fixed.

Not folded (intentionally orthogonal): excalidraw (.excalidraw JSON), p5js
(generative canvas), claude-design / popular-web-designs / design-md (visual
design taste / brand vocab / token spec).

* feat(skills): ship html-effectiveness gallery as fetched reference examples

Add scripts/fetch-examples.sh (idempotent clone/pull of Anthropic's MIT
html-effectiveness gallery) + references/examples.md mapping each of the 20
example files to a mode so the agent reads the right worked example. The clone
lands in references/examples/ and is gitignored (it's a 384KB upstream repo,
not vendored). SKILL.md workflow + reference list now point at it; falls back to
the distilled pattern references when offline.

* feat(skills): make reading a gallery example a required authoring step

Reading the matching html-effectiveness example is now workflow step 2 (was an
optional aside in step 3): fetch the gallery, read_file the file for your mode,
mirror its structure. Models skip optional steps; the examples are the ground
truth, so consulting one is mandatory. Added an 'Example' column to the
mode->build quick-reference table and a 'don't skip the example' pitfall.

Also dogfooded the skill: read 03-code-review-pr.html and 13-flowchart-diagram.html
raw and reconciled the distilled references against source — aligned diff-row tint
opacity to the source's 0.15 (was 0.18) and added the .ctx/.hunk rows in
house-style.md + base.html so they match 03-code-review-pr.html verbatim.

* docs(skills): explain the consolidation + bundled-vs-optional rationale

The supersession note only stated *what* was folded, not *why* the prune is
sound. Expand SKILL.md's intro into a 'Why this skill exists' section: the three
former skills emitted the same artifact and overlapped, so consolidating removes
which-one-do-I-load ambiguity; and the optional->bundled promotion of
concept-diagrams is footprint-safe because this skill has zero deps (only cost is
the 60-char description; everything else is progressive-disclosure). States the
bundling dividing line explicitly: zero install cost + broadly useful gets
bundled, real install cost (hyperframes: Node+FFmpeg+Chromium) stays optional.

Regenerated website per-skill page to match.

website/docs/user-guide/skills/bundled/software-development/software-development-python-debugpy.md

@@ -21,7 +21,7 @@ Debug Python: pdb REPL + debugpy remote (DAP).
 | License | MIT |
 | Platforms | linux, macos |
 | Tags | `debugging`, `python`, `pdb`, `debugpy`, `breakpoints`, `dap`, `post-mortem` |
-| Related skills | [`systematic-debugging`](/docs/user-guide/skills/bundled/software-development/software-development-systematic-debugging), [`node-inspect-debugger`](/docs/user-guide/skills/bundled/software-development/software-development-node-inspect-debugger), [`debugging-hermes-tui-commands`](/docs/user-guide/skills/bundled/software-development/software-development-debugging-hermes-tui-commands) |
+| Related skills | [`systematic-debugging`](/docs/user-guide/skills/bundled/software-development/software-development-systematic-debugging), [`node-inspect-debugger`](/docs/user-guide/skills/bundled/software-development/software-development-node-inspect-debugger), `debugging-hermes-tui-commands` |
 
 ## Reference: full SKILL.md