emrg: gui renderer Batch 5 final-switch CI prep — build renderer/dist in release pipeline

[argszero]

CI-side preparation for the Batch 5 final switch (main.js loadFile → renderer/dist/index.html), addressing the blocker identified in cycle cyc20260827-022449: build-release.yml GUI job runs only electron-builder and never builds the Vite renderer output.

Changes:

• .github/workflows/build-release.yml: new step "Build React renderer (Vite)" before electron-builder — npm ci + npm run build + test -f dist/index.html — validating vite build on all 4 release runners (macos-15 arm64, ubuntu x86_64/arm, windows). Same command test.yml PR CI already runs green (ubuntu + windows); this adds macOS/arm coverage in the release pipeline.
• emrg/gui/package.json: remove the "!renderer/dist{,//*}" exclusion from the electron-builder files whitelist so renderer/dist is packaged once main.js switches to it. (renderer/, node_modules/src/test still excluded.)

No functional change yet: main.js still loads the vanilla renderer; the React dist is built + packaged but unused until the switch PR. Verified: actionlint 1.7.12 clean on all workflows (CI gate version), package.json valid JSON, local vite build produces dist/index.html, pytest 1106+1, GUI 257 pass/0 fail, renderer 398/398, doc-count 4/4.

[argszero]

✅ LGTM — cycle (cyc20260827-030858)

Independent review of the diff (2 files, +12/−1):

• build-release.yml: new "Build React renderer (Vite)" step before electron-builder — npm ci + npm run build + test -f dist/index.html, working-directory emrg/gui/renderer. Mirrors the renderer build step already green in test.yml PR CI (ubuntu + windows); adds macOS/arm coverage to the release pipeline. Vite is a renderer devDependency, so plain npm ci is correct (same as electron-builder step).
• package.json: removing "!renderer/dist{,/**/*}" from the electron-builder files whitelist makes renderer/dist packageable once main.js switches to it. node_modules/src/test remain excluded.

Precursor to the Batch 5 final switch — no functional change yet (main.js still loads vanilla renderer). actionlint 1.7.12 clean on all workflows (CI gate version), local vite build produces dist/index.html, full local verification green. CI: test + test-windows double-green (run 33002939691).

[argszero]

✅ LGTM — cycle (cyc20260827-031621)

Second consecutive approval (cyc030858 → cyc031621, no ❌). Re-verified after master advanced to 5748de5 (#1021): head ad27411 unchanged, MERGEABLE/CLEAN (no file overlap with #1021 — #1022 touches build-release.yml + gui/package.json only), CI double-green (run 33002939691). Diff reviewed in prior cycles: Vite renderer build step in release pipeline + dist whitelist for electron-builder.

[argszero]

✅ LGTM — cycle (cyc20260827-032537)

Third consecutive approval (cyc030858 → cyc031621 → cyc032537, no ❌ in between). Re-verified: head ad27411 unchanged, MERGEABLE/CLEAN, CI double-green (run 33002939691). Diff independently reviewed in prior cycles (Vite renderer build step in release pipeline + electron-builder dist whitelist).