feat(agentos): install ordinary apps at runtime

[siwei-yuan]

Summary

• Decouple ordinary Apps from firmware: firmware contains only the resident Pi Agent System App.
• Build any ordinary App as one .pocketapp with exact declared credentials, then install it through one native Installer contract.
• Add the current LAN HTTP ingress and Pi Design review/installing/success/failure UI without adding a second lifecycle path.
• Keep Pi Agent resident while ordinary View and Data Guests load on demand in separate simple 3-entry LRU caches.
• Allocate App QuickJS heaps and large ESP32 worker stacks from PSRAM through the host-selected PocketJS allocator API.

Architecture boundaries

• HTTP only transports the complete artifact. Installer alone validates the package, stores credentials in NVS, creates current, updates the in-memory installed-App index, schedules, and the live Tool snapshot.
• A future UART ingress must hand the same artifact to Installer and cannot write lifecycle state directly.
• Installation does not foreground the new App; the user remains on the install screen until dismissing it.
• Marketplace, Registry, signing, TLS, update, rollback, uninstall, migration, and credential UI remain out of scope.

Cleanup

• Delete the old pocket-pi-app-pack embedded ordinary-App composition.
• Delete factory seeding, build-time ordinary-App selection, App whitelist logic, and UART App-credential injection.
• Pin all PocketJS crates to merged commit e12cf12f82cc60b636368119d49a06eb9ed2a3d5 and remove both local path patches.
• Rename the single System App build command from agentos-apps to pi-agent.
• Update architecture, App, ESP32, Pi Design, credential, LRU, ingress, provenance, and build documentation. The root README now warns that breaking changes are frequent during rapid development.

Validation

• cargo test --workspace — 34 passed
• bun test apps/_shared/text.test.ts — 3 passed
• cargo clippy --workspace --all-targets -- -D warnings — passed
• cargo fmt --all -- --check — passed
• git diff --check — passed
• cargo xtask build pi-agent against the pinned PocketJS commit — passed
• Exa and Robinhood package builds with test-only exact-ID credential files — passed
• cargo xtask build esp32-p4 release build against the pinned PocketJS commit — passed

A fresh post-commit physical-board upload, provider call, reboot-persistence run, and sustained memory-pressure run remain separate hardware acceptance tiers; this PR does not treat the cross-build as those proofs.