feat: fail-closed per-task Hyperagent budgets

[Shifat7]

What changed

Daily caps bound a whole day; runaway agent loops happen per task. Adds durable named tasks with their own budgets:

• hacb task start <name> / hacb task status / hacb task stop (src/cli.mjs)
• Durable state in /tasks.json behind the existing file-lock pattern (src/config.mjs): startTask, getActiveTask, stopTask, reserveTaskRequest, commitTaskToolLoop
• Bridge enforcement (src/bridge.mjs): after the daily reservation succeeds, requests count against the active task. Exhaustion fails closed with exactly: "This local Hyperagent task budget is exhausted. Start a new task or raise maxRequestsPerTask." — and releases the unused daily slot so nothing leaks.

Config: maxRequestsPerTask (8), maxPromptCharsPerTask (180000), warnAtPromptCharsPerTask (120000 → audit task_budget_warning).

Guarantees (test-enforced):

• Budgets persist across process restarts.
• Per-task budget is separate from — and can never bypass — the daily budget.
• Requests without an active task are unaffected.
• Counting + fail-closed behaviour covered at both module and HTTP levels.

Testing

npm test: 81 pass, 0 fail (3 pre-existing skips). New files: test/task-budget.test.mjs; bridge-level 200→429 flow asserts the daily slot was released.