fix: resolve four bug reports (#2290, #2282, #2276, #2272)

- #2290 suggest-compact: honor ECC_CONTEXT_WINDOW_TOKENS / CLAUDE_CODE_AUTO_COMPACT_WINDOW
  so 400k-window models (Opus 4.x) no longer report ~double context usage; add
  override + isolation tests in transcript-context.test.js.
- #2282 install: bare-language syntax is legacy-only by design, but the error
  now distinguishes a supported-but-wrong-mode target (gemini/codex/…) from a
  genuinely unknown one and points to --profile/--modules/--skills.
- #2276 cost-report: the command + cost-tracking skill targeted a SQLite DB no
  tracker writes. Repoint both at the real ~/.claude/metrics/costs.jsonl (JSONL,
  estimated_cost_usd), reduce cumulative-per-session snapshots to latest-per-session,
  and use node instead of sqlite3 for cross-platform support.
- #2272 gateguard: make the 'confirm no existing file' checklist item
  tool-agnostic (Glob/Grep or find/grep via Bash) so hosts without a Glob tool
  don't get a dead tool call.

Full suite 2839/2839; lint green.

docs/COMMAND-REGISTRY.json

@@ -49,7 +49,7 @@
     },
     {
       "command": "cost-report",
-      "description": "Generate a local Claude Code cost report from a cost-tracker SQLite database.",
+      "description": "Generate a local Claude Code cost report from the ECC cost-tracker metrics log.",
       "type": "testing",
       "primaryAgents": [],
       "allAgents": [],