feat: add route-aware pricing estimates (salvaged from #1563)

[teknium1]

Summary

Salvaged from PR #1563 by @kshitijk4poor. Cherry-picked their 3 commits onto current main with conflict resolution and follow-up fixes.

Replaces the static MODEL_PRICING dict + keyword heuristic cost calculation with a proper route-aware pricing architecture:

• Canonical usage normalization — normalize_usage() handles Anthropic, OpenAI, and Codex API shapes, splitting tokens into input/output/cache_read/cache_write/reasoning buckets
• Route-aware pricing — resolve_billing_route() determines pricing based on provider+model pair, not just model name heuristics
• Cache-aware billing — separate per-million rates for cache read/write tokens instead of lumping into input
• Cost status tracking — CostStatus (actual/estimated/included/unknown) and CostSource for transparency
• OpenRouter live pricing — fetches from OpenRouter models API, converts per-token to per-million rates
• Subscription-included routes — marks openai-codex as included (cost $0)
• Schema migration v4→v5 — adds cache_read_tokens, cache_write_tokens, billing_provider, billing_base_url, estimated_cost_usd, actual_cost_usd, cost_status, cost_source, pricing_version columns
• Backward-compatible wrappers — get_pricing() and estimate_cost_usd() still work for callers that haven't been updated

Follow-up changes (on top of cherry-pick)

• Removed speculative forward-looking pricing entries (claude-opus-4.6, gpt-5, gpt-5.4, o4-mini) — show 'unknown' instead of inventing prices
• Removed cost $$ display from CLI status bar entirely
• Made OpenRouter metadata pre-warm non-blocking (threaded)
• Fixed duplicate fetch_model_metadata import
• Resolved conflicts in hermes_state.py (preserved with self._lock) and run_agent.py (normalize_usage replaces inline Anthropic cache handling)

Test plan

• python -m pytest tests/ -n0 -q — 4992 passed (16 pre-existing failures unrelated to this PR)
• Specifically verified: tests/agent/test_usage_pricing.py, tests/test_cli_status_bar.py, tests/test_insights.py, tests/test_hermes_state.py, tests/gateway/test_session.py, tests/gateway/test_status_command.py — all 229 pass

Attribution

Original work by @kshitijk4poor in PR #1563 (3 commits cherry-picked with authorship preserved).