Persist Code Mode MCP UI state and harden gateway reconciliation

[jmagar]

Summary

• install the complete Chromium runtime dependency set in Gateway Admin CI while continuing to use the runner image's cached Playwright browser
• move Code Mode MCP App visibility into shared persisted runtime state
• add labby gateway code ui status|enable|disable and gateway.code_mode.set API support
• make MCP mcp_app changes persist across sessions and restarts
• hide disabled Code Mode app resources from both discovery and cached direct reads
• avoid cold-connecting or rebuilding upstreams for UI-only visibility changes
• preserve the previous live gateway snapshot until reconciliation completes, fixing add/update/remove/import and Code Mode catalog diff detection
• add stable notification attribution for gateway.code_mode.set and mcp.call.mcp_app

Review fixes

• blocked cached normal, history, Skybridge, and versioned Code Mode UI resource reads while disabled
• modeled the stable synthetic codemode tool so raw-to-Code-Mode transitions notify even with no upstreams
• split config-file persistence from in-memory installation so reload diffs compare old and new configurations correctly
• added live-pool add/update/remove reconciliation coverage and exact catalog notification assertions

Validation

• canonical just lint: passed, including workspace clippy with -D warnings, formatting, skill drift, Cargo wrapper, and toolchain sync
• generated docs: 15/15 fresh
• actionlint .github/workflows/ci.yml: passed
• Gateway Admin cached Chromium launch: passed
• Gateway Admin browser tests: 5/5 passed
• labby-runtime: 49/49 passed
• labby-gateway: 572 passed, 3 ignored
• gateway no-default feature slice nextest: 980/980 passed, 3 skipped
• workspace all-features nextest CI profile: 2170/2170 passed, 7 skipped
• MCP resource handlers: 42/42 passed
• MCP tool handlers: 73/73 passed
• locked workspace and extracted-crate compile matrices: passed