refactor(cli): extract usage/insights cluster into CLIUsageMixin (cli.py god-file slice R4)

[andrexibiza]

Summary

cli.py god-file slice R4: extract the usage/insights/context-display cluster from cli.py into hermes_cli/cli_usage_mixin.py (class CLIUsageMixin). Part of the repo-wide large-file decomposition (tracker #78647).

What changed and why

• Usage/insights cluster (window 11202–11442, 241 lines, 5 members: _handle_usage_command, _usage_reset, _show_context_breakdown, _show_usage, _show_insights) moved byte-verbatim (golden sha e117ff8728… confirmed)
• True read-only slice: zero self-writes to cli.py module globals (verified — the consensus lane caught pass A's wrong claims about the window boundaries)
• One sanctioned seam edit: lazy from cli import format_duration_compact inside _show_usage (pure function, documented in module docstring)
• CLIUsageMixin appended last to HermesCLI bases; _manual_compress stays in cli.py (explicit R3-consensus deferral)
• Double-blind: 2 analysts → consensus (R4-CONSENSUS.md, 5-member window won over 6-member) → implementer → 2 blind re-reviewers (both APPROVED; EOF blank-line MINOR fixed in a follow-up hygiene commit 38d5b61b24)

Testing

• test_cli_usage_seam.py: 14 passed (identity asserts 5/5, no-back-import subprocess, usage reset, context-breakdown shape, insights aggregation)
• Static undefined-name scan: 0 real names in the moved module
• ruff clean · git diff --check clean (after hygiene fix) · LF-only · DCO signed

Coordination / interlock

• Epic: Part of [COMPLETE] Large-file decomposition: 20/20 done #78647 · Target: Part of Refactor cli.py God-File (UI & Commands Extraction) #55136
• Sibling PRs: the 3 other cli.py wave-1 slices — disjoint windows
• Dedup: no existing PR extracts the usage/insights cluster

Part of #78647
Part of #55136

[andrexibiza]

🔒 This shard is part of the cli.py KILL LOCK — the permanent record of the 18,485-line whole, the mess it caused (#54960 duplicate-tracking chaos, #65303 no ESC-interrupt, #72797 XML-tag loss, #75461 redaction bypass, #76914 unfinalized sessions, #77764 approval truncation, #39446 /reload-mcp blocking, terminal-escape leaks), every shard in the wave, the #12355 block on R1, and every open fixer PR still fighting the surface (#73104 #75476 #77776 #75084 #76804 #76995 #71295 #78871 #74491 #72821 #57453 #61429 #71027 #62027 #65192 #71088 #74038 #69918 #67484 #12355 #75207 #32193 #74281 #37818 #27172 #65785).

Lock: posted on #55136 · Indexed by the Kill All Gods meta-issue #78647.