feat(web): serve gatherer quota-current on /quota (#1151) - #1329

Final visibility hop for the quota plane (#1151): the aggregator overlay reads quota-current.json (written by the gatherer into the deployed aggregator dir on its 15-min tick) and applies it to the quota view.

• Fresh (<=20 min) ok entries take precedence for the pool whose id equals the entry serviceId: percent windows replace dated-read windows, pool state + choices recomputed.
• Error / aged entries surface as the pool's state (error/stale, with the reason) via a new pool freshness stamp — never zeros, never silently presented as current.
• /api/quota.json stays additive: pools gain freshness; a top-level gatherer summary (tick time, health, per-provider freshness incl. pool-less providers like OpenCode Go / Antigravity) rides along.
• /quota pool cards show the gatherer freshness line (state, measured-at, source, error).
• Config: PM_AGG_QUOTA_CURRENT_FILE (default quota-current.json in the aggregator cwd).

Known remaining gaps (documented, not hidden): OpenCode Go still arrives as one combined gatherer row (serviceId opencode-go) with no per-workspace pool to overlay, and Antigravity arrives per-model — both appear in the gatherer summary but do not overlay the split pools until the quota module splits them.

Tests + live verification results land on #1151.

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