feat(observatory): raw-WebGPU living cognitive field with 5 deterministic demos

The Observatory is a full-bleed, zero-library WebGPU surface that renders
the memory graph as a living cognitive field. Five deterministic demo
moments driven by a URL contract (?demo=<name>&seed=...&frame=N):
recall-path, engram-birth, salience-rescue, forgetting-horizon, firewall.
Capture mode (?frame=N) freezes the sim deterministically so the same URL
produces identical pixels, the viral-clip primitive.

Architecture: bare-metal WebGPU engine (no Three.js), seeded demo clock,
per-demo plan + renderer modules, WGSL shaders (simulate, nodes, edges,
path, birth particles, rescue, forgetting, firewall) plus a post-processing
chain (tone mapping, MIP). DOM is instrument overlays only (telemetry strip,
timeline spine, rescue verdict); the layout gives /observatory the same
full-bleed bypass as marketing routes so recordings stay clean.

Reads the real memory graph. Verified live: svelte-check 939 files 0 errors,
96 observatory unit tests green, all 5 demos load at 108-119fps with zero
console errors against the live brain.

Known follow-up: engram-birth capture-mode particle cluster needs a render
fix pass before it is camera-ready; the other 4 demos are camera-ready.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/causebench-recall-at-1.svg

@@ -0,0 +1,46 @@
+<svg viewBox="0 0 680 430" xmlns="http://www.w3.org/2000/svg" width="680" height="430" role="img" aria-label="CauseBench root-cause recall at 1: Vestige scores 60% on synthetic and 50% on real; Dense vector, Hybrid-RRF, BM25, TF-IDF and Recency all score 0%." font-family="-apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif">
+  <title>CauseBench root-cause recall@1 — Vestige 60% / 50%, every resemblance retriever 0%</title>
+
+  <text x="24" y="34" font-size="17" font-weight="600" fill="#1d9e75">Root-cause recall@1 — can the retriever rank the true cause #1?</text>
+  <text x="24" y="56" font-size="13" fill="#888780">CauseBench · a cause that shares an entity with the failure but none of its words</text>
+
+  <line x1="330" y1="78" x2="330" y2="308" stroke="#88878055" stroke-width="1"/>
+  <line x1="450" y1="78" x2="450" y2="308" stroke="#88878055" stroke-width="1"/>
+  <line x1="570" y1="78" x2="570" y2="308" stroke="#88878055" stroke-width="1"/>
+  <line x1="210" y1="78" x2="210" y2="308" stroke="#888780" stroke-width="1.5"/>
+
+  <text x="210" y="330" font-size="11" fill="#888780" text-anchor="middle">0%</text>
+  <text x="330" y="330" font-size="11" fill="#888780" text-anchor="middle">20%</text>
+  <text x="450" y="330" font-size="11" fill="#888780" text-anchor="middle">40%</text>
+  <text x="570" y="330" font-size="11" fill="#888780" text-anchor="middle">60%</text>
+
+  <text x="196" y="99" font-size="13" font-weight="600" fill="#0f6e56" text-anchor="end">Vestige</text>
+  <rect x="210" y="88" width="216" height="17" rx="4" fill="#1d9e75"/>
+  <rect x="210" y="109" width="180" height="17" rx="4" fill="#5dcaa5"/>
+  <text x="434" y="101" font-size="12" font-weight="600" fill="#0f6e56">60% synthetic</text>
+  <text x="398" y="122" font-size="12" fill="#0f6e56">50% real</text>
+
+  <text x="196" y="158" font-size="13" fill="#888780" text-anchor="end">Dense vector (nomic)</text>
+  <circle cx="212" cy="153" r="2.5" fill="#888780"/>
+  <text x="224" y="157" font-size="12" fill="#888780">0%</text>
+
+  <text x="196" y="191" font-size="13" fill="#888780" text-anchor="end">Hybrid-RRF (BM25 + dense)</text>
+  <circle cx="212" cy="186" r="2.5" fill="#888780"/>
+  <text x="224" y="190" font-size="12" fill="#888780">0%</text>
+
+  <text x="196" y="224" font-size="13" fill="#888780" text-anchor="end">BM25</text>
+  <circle cx="212" cy="219" r="2.5" fill="#888780"/>
+  <text x="224" y="223" font-size="12" fill="#888780">0%</text>
+
+  <text x="196" y="257" font-size="13" fill="#888780" text-anchor="end">TF-IDF</text>
+  <circle cx="212" cy="252" r="2.5" fill="#888780"/>
+  <text x="224" y="256" font-size="12" fill="#888780">0%</text>
+
+  <text x="196" y="290" font-size="13" fill="#888780" text-anchor="end">Recency</text>
+  <circle cx="212" cy="285" r="2.5" fill="#888780"/>
+  <text x="224" y="289" font-size="12" fill="#888780">0%</text>
+
+  <line x1="24" y1="356" x2="656" y2="356" stroke="#88878040" stroke-width="1"/>
+  <text x="24" y="380" font-size="12" fill="#888780">Every resemblance retriever ranks the true cause #1 exactly 0% of the time.</text>
+  <text x="24" y="400" font-size="11" fill="#888780">Vestige also lands the cause in the top 5 in 100% of cases. Source: benchmarks/causebench/RESULTS.md · reproduce with 3 commands.</text>
+</svg>