v0.9.2 — portability scaffold

Internal scaffolding for future platform portability work. No user-facing behavior change — Claude plugin, Custom GPT, and Gemini Gem adapters all behave identically.

What's new

• platforms/model-agnostic/ — portable counseling kernel (core-instructions.md, runtime-capability-matrix.md, adapter-contract.md) that platform adapters derive from.
• scripts/check-portability.sh — static guard that fails when the model-agnostic core contains platform-specific runtime terms.
• tests/portability/README.md — five canonical scenarios for cross-adapter behavior checks.
• Parity tier vocabulary: core counseling parity, workflow parity, safety parity. platforms/README.md, platforms/custom-gpt/PARITY.md, and platforms/gemini-gem/README.md now reference them explicitly.
• Adapter provenance notes in platforms/custom-gpt/instructions.md and platforms/gemini-gem/instructions.md.
• platforms/SYNC_LOG.md tracks the new model-agnostic core separately.

What did not change

• skills/college-navigator/SKILL.md, .claude-plugin/plugin.json, commands/, agents/, and hooks/ are untouched.
• The full Claude plugin remains the reference implementation.

Follow-up work (not in this release)

• Refactor SKILL.md to a concise orchestration layer with detail in references.
• Add fixture-based tests for the privacy hook.
• Build scenario benchmarks under tests/scenarios/.