fix(llm): populate usage for the Claude Code local-agent path (#140)

* fix(llm): populate usage for the Claude Code local-agent path

LocalAgentAdapter.chat() never set `usage` on its LLMResponse, so
AgentLoop's token budget check (tokensUsed >= maxTokens) silently
never fired for Claude Code missions. maxIterations was the only
brake, and it bounds turn count, not actual spend.

Claude Code's --output-format json (instead of text) returns exact
per-call token counts, including prompt-cache creation/read tokens
that a text-length estimate has no way to see. localAgentChat now
requests that format for the claude agent id only. LocalAgentAdapter
parses the envelope into usage.promptTokens/completionTokens, with a
character-based estimate as a fallback if parsing fails, so usage
never goes back to undefined.

Verified directly against the CLI: a live run now reports
promptTokens 24458, completionTokens 1662 instead of undefined/0.
Full suite: 675/675, no regressions.

Fixes #139

* test(llm): harden Claude usage fallback

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Co-authored-by: Joseph Magly <1159087+jmagly@users.noreply.github.com>