[vogelsgesang]

Switch the monorepo from Yarn (classic) to pnpm and modernize CI.

Package manager and workspace:

• Add packageManager: pnpm@11.21.0 and engines.node >=24 (the repo previously pinned neither; CI ran on Node ^20.18.0, so this also raises the Node floor to 24).
• Replace the root workspaces array with pnpm-workspace.yaml; the members (query-graphs, standalone-app, upload-server) are unchanged. plan-dumper is a Python tool and is intentionally not a workspace member.
• Point standalone-app at the core library via workspace:^.
• Remove yarn.lock and regenerate pnpm-lock.yaml; this bumped all dependency versions to the latest version within the declared ranges.
• Add .pnpm-store to .gitignore.

Declare missing dependencies that Yarn's hoisting had masked (pnpm's isolated node_modules surfaces them as errors):

• root: @eslint/js and globals (imported by the ESLint flat config).
• query-graphs: @types/react and @types/react-dom (needed for the library's declaration emit; otherwise tsc fails with TS2742 under pnpm's non-hoisted layout).

CI (.github/workflows/ci.yaml):

• Replace the manual yarn cache (actions/cache plus the deprecated ::set-output dance) with pnpm/action-setup and setup-node's cache: 'pnpm'; pin node-version: 24.
• Install with pnpm install --frozen-lockfile; build all modules with a single pnpm -r build, which pnpm runs in workspace-dependency order (query-graphs before standalone-app), replacing the two per-module build steps.
• Bump peaceiris/actions-gh-pages v3 -> v4.

Other:

• Fix the query-graphs clean script: it ran rimraf dist/, but the tsc outDir is lib/, so it never removed the build output or the incremental tsconfig.tsbuildinfo. Point it at lib/ and the buildinfo so a clean actually forces a fresh tsc --build.
• media: give the logo SVG unitless (px) width/height matching its viewBox instead of millimetre units. The freshly-resolved, newer sharp (pulled in via favicons) rasterizes mm-unit SVGs at a size that grows quadratically with the requested density, overshooting sharp's input-pixel limit on the large iOS appleStartup splash images and failing the build. Unitless dimensions scale linearly and render identically (the app sizes the logo via CSS).
• Reformat one line in postgres.ts (flagged by newer Prettier).
• Update the developer docs and agent guide to reference pnpm.