README: original-art poster + dark-mode wordmark via prefers-color-scheme

Context

Follow-up to #15671 / PR #15672 (merged 65fd583458): Tobi reports two post-merge regressions and keeps ticket/PR work delegated (Emmy A2A 00:46Z). (a) The live YouTube maxresdefault.jpg poster carries the Devpost center-crop compromise; the GitHub README shows the full frame, so the original, aesthetically stronger 16:9 poster should serve instead. (b) The header wordmark neo_logo_text_primary.svg has black text — illegible in GitHub dark mode (screenshot receipt on file); neo_logo_text_secondary.svg is also black and neo_logo_white.svg is the icon-only mark (157×157, verified), so no dark-mode text wordmark exists.

The Problem

1. Poster: the README depends on YouTube's live thumbnail (center-cropped for Devpost) rather than the original poster art.
2. Wordmark: black-on-dark header logo for every GitHub dark-mode visitor.

V-B-A Receipts (pre-flight, this session)

• Original poster verified at Emmy's seat copy: 3840×2160, SHA-256 f757a6bbbddbbdf6ea05e12801e43559976cf99aaa778a5a1c94077e1231a3fd — matches her receipt exactly. (test-results/ is gitignored → an optimized committed copy is required.)
• resources/images/logo/neo_logo_text_primary.svg: root fill="none"; the wordmark text path carries explicit fill="black"; the two mark triangles inherit the root fill="none" (hollow) with stroke="#3E63DD" — Emmy's source-level correction at issuecomment-5040600811 (my initial read had them default-filling black; fill is an inheritable presentation attribute, root none reaches the paths).
• GitHub officially supports <picture><source media="(prefers-color-scheme: dark)"> in READMEs.

The Fix

1. Poster: resample the original to 1920×1080 JPEG (README renders ~851px; 2x retina headroom), commit as resources/images/readme/neo-agent-fleet-manager-poster.jpg, point the poster <img> at the repo-owned relative path. Keep the YouTube link + visible caption unchanged.
2. Dark wordmark: add resources/images/logo/neo_logo_text_primary_dark.svg — the primary asset with ONLY the wordmark text fill flipped to white; the mark triangles keep the inherited hollow interior + #3E63DD stroke (logo geometry preserved; a mark-fill flip was rejected via review correction). Header line 3 becomes <picture> + prefers-color-scheme sources, primary asset preserved as the light/default <img>. Repo-owned relative paths so README + assets land atomically in one PR.
3. Render-check BOTH GitHub themes (light + dark Playwright color-scheme emulation against the branch README) before opening the PR; receipts in the PR body.

Acceptance Criteria

• Poster serves the committed 1920×1080 original-art copy via repo-relative path; YouTube link/caption intact
• Dark wordmark variant committed with hollow mark interiors preserved; header uses <picture> + prefers-color-scheme with primary as light/default
• Branch README render-checked in light AND dark emulation (wordmark legible in both; receipts posted)
• No test-results/ dependency; no pages-repo dependency for the changed assets
• Identity framing untouched

Out of Scope

• Thumbnail/poster redesign (asset is operator-selected and hash-pinned)
• Pages-repo asset migration beyond these two surfaces
• Any README prose change

Related

• #15671, PR #15672 (the hero swap this follows up)
• D#15570 (film production; poster art origin)

Live latest-open sweep: checked latest 20 open issues at 2026-07-22T00:50Z; no equivalent found. A2A in-flight sweep: Emmy's operator-delegation assigns this scope to me; no competing claim.

Origin Session ID: 72c8c42d-f18a-408c-97c8-aeb1f82dd276

Retrieval Hint: "README dark mode wordmark picture prefers-color-scheme poster original art committed copy"