Simplify internal modules and daily development commands

[tiammomo]

Large ledger and model-management modules mixed unrelated responsibilities, while native lifecycle and verification procedures were repeated across scripts and documentation. This change gives credential management its own component, separates ledger reporting from transaction orchestration, and makes scripts/dev.sh help the starting point for daily source development.

• Move unchanged ledger reporting methods into enterprise_ledger/reporting.rs and keep operations validation helpers with their consumers. The ledger entry module shrinks from 9,156 to 7,939 lines.
• Move provider credential forms, mutations and dialogs out of ModelsPage (2,798 to 2,360 lines). Share credential readiness and active-account selection, including the routing overview's previously missed usable credential-pool fallback.
• Centralize native run/start/stop/restart/status/logs/validate/doctor/check commands and Rust checks. Preserve legacy script entry points. Stop only binaries belonging to the current checkout; refuse duplicate starts for unhealthy owned processes and identify responding unmanaged endpoints.
• Resolve source commands from the checkout directory, build only the native gateway when requested, and fix the compiler-discovery fallback's erroneous failure when conventional compilers are absent.
• Keep detailed setup and troubleshooting procedures in the development guide, removing 80 documentation lines overall. The 25 tracked root entries stay unchanged.

Validation: scripts/check-all.sh passed with 475 Rust tests, 128 dashboard unit tests, 15 lifecycle/freshness tests, formatting, Clippy, ShellCheck, documentation links, configuration examples, and Runtime Adapter fixtures. All 21 Playwright tests passed against a real disposable PostgreSQL database, including credential validation/create/edit/delete. Targeted PostgreSQL migration, state, aggregation, concurrent admission and operations tests also passed. Native start/status/smoke/stop were exercised locally; dashboard dependency audit reported no vulnerabilities. No paid upstream requests were made.

The changes are organized into four commits covering ledger responsibilities, credential management, developer commands, and documentation. There are no dependency or schema changes.