fix(build): Astryx surface inventory cannot see most of the design system

[Astro-Han]

Problem

#3064 made the inventory check symmetric and #3646 kept it globally enforced. Both fixed the plumbing — whether the two halves agree and whether the gate runs. This is the third gap in the same file, and it is semantic: what the gate is able to detect at all.

The severity model only recognizes raw interactive primitives:

if (rawButton || rawInput || rawSelect) severity = 'blocker';
else if (rawTextarea) severity = 'polish';

1. A hand-rolled replacement for a shipped Astryx component scores aligned. It renders no raw control, so it is indistinguishable from a genuinely aligned file — and the inventory then certifies it. A surface added this way reads | … | none | aligned — no raw controls; no Astryx JSX usage | aligned |, moving the totals from aligned 212 to aligned 213. The rule as stated in docs/astryx-alignment-inventory.md:36 is "Raw <button> / <input> / <select> with Astryx twin" — it covers wrong primitive, not redundant component.

2. ASTRYX_COMPONENTS is a hand-maintained second representation of what Astryx ships. It holds 47 names; @astryxdesign/core/dist has 107 component directories. Timestamp is absent, so it appears 0 times across all 214 rows even though packages/ui/src/chat-turn.tsx imports and renders it. ChatMessage, ChatMessageMetadata, and Thumbnail are invisible the same way — so removing an Astryx component from a file leaves its row byte-identical, which is how this surfaced.

Desired outcome

• Derive the known-component set from @astryxdesign/core instead of maintaining a second list, so the "Astryx used" column is a true record and design-system additions are picked up without a manual edit. This is the same root cause Astryx surface inventory check is one-directional and not wired into CI #3064 identified — a generated artifact whose input is hand-maintained drifts in whichever half the author forgets.
• Add a severity tier for "re-implements a component Astryx already provides", so swapping an Astryx component for a local equivalent is visible in review.

Found while reviewing #3681.

AI use: Claude Code assisted with source and issue investigation; the analysis and conclusions are my own.