feat: add safe portal plugin routes

[TrueKrishna]

Summary

• add a validated portalRoutes deployment contract for session and signed-upstream plugins
• derive private upstream addresses for Docker, Fly, and AWS instead of accepting operator-supplied routing JSON
• proxy browser plugins with verified sessions and signed portal identity
• proxy qm.edge.v1 machine traffic without a human session through a strict header allowlist

Security boundary

• built-in and overlapping path prefixes are rejected
• only private HTTP(S) origins are accepted at portal startup
• PORTAL_PLUGIN_ROUTES is deployment-managed and cannot be overridden
• signed machine routes drop cookies and all human/portal identity headers

Verification

• npm --prefix cli test
• npm --prefix cli run typecheck
• npm --prefix cli run build
• npm --prefix plugins/portal test (108 passed)
• npm --prefix plugins/portal run typecheck

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[TrueKrishna]

Production deployment surfaced newly published advisories in the mandatory core-image npm audit. I added commit 50f8e59, which refreshes brace-expansion, fast-uri, Hono, and undici; the Pi tarball needed a new shrinkwrapped security.3 asset because its nested shrinkwrap intentionally ignores root overrides.

Verification: clean root npm ci, npm audit --omit=dev --audit-level=moderate (0 vulnerabilities), test/pi-dependency-security.test.ts (2/2), and npm run typecheck. Security.3 asset: https://github.com/TrueKrishna/pi/releases/tag/qm-pi-coding-agent-0.82.0-security.3