Centralize injectable platform facts used by detection and providers

[stalep]

Review of terminal-detect, terminal-api, and terminal-tty at 859020a6 on 2026-09-28.

Review item: Design 5: platform context
Priority: P2
Evidence: Duplicated platform/environment decisions confirmed in source.

Problem / scope

OSUtils, TerminalDetector, IdeThemeDetector and native transports use different
mixtures of static OS constants, environment scans, system properties and
runtime handle checks. This complicates cross-host tests and can conflate an
environment hint with proof that a particular descriptor is a terminal.

Evaluate a small immutable/injectable platform context with live descriptor
checks at the I/O boundary. Do not assume a wholesale public OSUtils move is
required or create a terminal-detect -> terminal-api dependency.

Source at the reviewed commit

• terminal-api/src/main/java/org/aesh/terminal/utils/OSUtils.java:27
• terminal-detect/src/main/java/org/aesh/terminal/detect/TerminalDetector.java:28
• terminal-detect/src/main/java/org/aesh/terminal/detect/IdeThemeDetector.java:56
• terminal-tty/src/main/java/org/aesh/terminal/tty/TtyDetect.java:81

Acceptance criteria

• Identify shared facts versus transport-specific live checks and choose a dependency-compatible home.
• Support host-independent OS/env/path test matrices without mutating JVM-global properties.
• Preserve public compatibility where practical and reduce repeated scans; keep the Java 8 baseline.

Tracking

Part of #300. Related: #296, #329, #330, #343, #347.