[codex] add dashboard LSP diagnostics

[ScriptedAlchemy]

Summary

Adds Phase 1 LSP-backed code diagnostics surfaced only in the TraceDecay dashboard.

• adds a dashboard-owned diagnostics broker with built-in language server adapters for Rust, TypeScript/JavaScript, Python, Go, C/C++, Objective-C, Zig, Lua, and PHP
• adds a Code Diagnostics dashboard plugin with per-language enable/disable controls, setup/install commands, command overrides, idle backfill controls, refresh actions, and diagnostic grouping by file
• adds dashboard API endpoints plus a CLI discovery command for available language servers and install hints
• keeps diagnostics isolated from model hooks/context paths for Phase 1

Validation

• npm run build --prefix dashboard
• git diff --check origin/split/self-improving-05-docs..HEAD
• CARGO_INCREMENTAL=0 cargo test --test lsp_code_diagnostics_test --test dashboard_code_diagnostics_api_test
• Earlier full Phase 1 smoke before publishing also covered cargo build, dashboard plugin asset route, CLI parser, tracedecay lsp servers --json, and a browser smoke with a temporary TypeScript error surfaced in Code Diagnostics.

Notes

Focused clippy remains blocked by unrelated pre-existing automation warnings in src/automation/config.rs and src/dashboard/automation_run_api.rs.

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[chatgpt-codex-connector]

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