feat(smith): trust provider input token usage

[edwin-zvs]

Summary

• make provider-reported input token usage authoritative for post-response context state, pruning, compaction, and learned-limit probes while retaining the character heuristic for preflight fallback and deltas
• add Anthropic prompt-cache breakpoints, cache-aware input occupancy, and configurable beta/context-window capabilities without changing compatible third-party defaults
• document the accounting and provider capability contracts in specs 0214 and 0215

Tests

• cargo test -p construct-adapter-smith (240 passed)
• cargo test -p construct-daemon config::tests (34 passed)
• cargo build
• git diff --check origin/main...HEAD

Visual evidence

Not useful for this internal provider/accounting and request-construction change; there is no direct UI surface.