[vicgupta]

Closes #236

Summary

Finishes the remaining work on #236 (the token budget itself landed in #246):

• --check limits line now shows the token limit: steps …, cost …, tokens …, time …, with the same (from config) / (from --token-limit) labels as the other limits.
• --init-config starter config has a commented token_limit: 0 line next to cost_limit.
• --attempts: --token-limit is now an invocation-wide budget, like --cost-limit and --time-limit. Each attempt gets the tokens left (--token-limit <remaining>), no new attempt starts once the budget is used up, and an attempt ending TokenLimitExceeded stops the run with stop reason budget exhausted. The --check plan line says "cost, token and time limits are shared by all attempts".
• --eval: suite tasks accept limits.token_limit, forwarded to each trial as --token-limit (validated >= 0).
• --workflow: token_limit is accepted in defaults and on each stage, forwarded as --token-limit (validated >= 0).
• Docs updated: docs/runs.md, docs/project-context.md, docs/eval-framework.md.

Decisions on open questions

• Turn cap stays off by default, per Vic's comment on the issue. No default-on step limit was added.
• In --attempts, the token limit is shared across attempts (matching how cost and time already work there) rather than applied per attempt. This is the safer reading of a budget; before this change the flag was forwarded verbatim, so each attempt got the full amount.
• In --eval, a top-level --token-limit keeps its current behaviour (forwarded to every trial as a per-trial cap). Only the per-task limits.token_limit key is new. A suite-wide token budget, like eval's --cost-limit, was not added, to avoid changing what an existing flag means for eval.
• All new token limits default to 0 (off), so existing configs, suites and workflows behave the same.

Testing

• gofmt -l . clean; go build ./..., go vet ./... and go test -count=1 ./... all pass.
• New tests (fakes only, no network or API keys): internal/attempts/token_budget_test.go, internal/harness/token_limit_test.go, internal/eval/token_limit_test.go, cmd/tinyagent/check_token_limit_test.go. Updated the existing --check limits-line expectations.