Harden configuration validation, toolbar selection, and regression coverage

[devmobasa]

Summary

Land the shared configuration, selection, runtime-error, and test infrastructure
changes before the session-persistence and clipboard-saving PRs.

This is a mixed foundation PR, not a config-only change.

Changes

Configuration validation

• Normalize non-finite loaded values to safe defaults.
• Share numeric bounds and click-highlight policy between the core app and configurator.
• Add an independent float-field inventory covering NaN, infinities, nested values, and containers.
• Preserve typed configuration conflict errors and clarify recovery behavior.
• Keep successful configuration loads from rewriting authored files.

Toolbar selection

• Resolve selected shapes once across property entries, text controls, and spotlight magnification.
• Preserve selection order, missing-ID handling, and locked-text behavior.
• Retain the tiny-selection fast path rather than hashing the entire frame.

Runtime errors and portal transport

• Preserve broker error categories across local and socket failures.
• Publish terminal session-dialog outcomes through the runtime controller.
• Exercise portal subscription transactions against a private D-Bus service.
• Replace broad dead-code suppression with narrowly documented exceptions.

Regression coverage and CI

• Strengthen image-admission, PNG/PDF export, rendered highlighting, and input-effect tests.
• Remove unnecessary test-only wrappers and duplicated fixture setup.
• Restore test environments through shared guards and keep temporary files under owned guards.
• Require Poppler for PDF artifact checks in CI.
• Strengthen shared-layer dependency checks, including grouped imports and raw identifiers.
• Discover domain sources recursively without relying on an exact source-file count.