feat: add compression context recovery hints

[ScriptedAlchemy]

Summary

• add a structured LCM context_recovery_hint when compression creates summary nodes
• surface that hint through the MCP compression response and preserve it through the Hermes bridge
• inject the model-visible recovery hint from Codex/Cursor sessionStart hooks when a session starts from compacted context
• document the behavior in the Codex and Cursor plugin READMEs

Validation

• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo fmt --all -- --check && git diff --check
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test compact_session_start
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test --test hooks_test
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test --test session_lcm_compression_test compress_in_transaction_baseline_decision_fixture_preserves_contract
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test --test mcp_handler_test lcm_compress_handler_honors_incremental_max_depth_override
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test --test hermes_lcm_bridge_test
• CARGO_TARGET_DIR=/tmp/tracedecay-cargo-target-pr72 cargo test --test agent_test test_codex_global_install_bundles_hooks_in_plugin

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Latest commit: 64d7c6b

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