Tune cold-cache tile bootstrap for faster initial map loads

[stef-k]

Summary

• BurstCapacity 10 → 12: 2 more tiles through on initial burst before sustained 2/sec rate
• AcquireTimeout 3.0s → 3.5s: 1 extra token per wave from replenishment, reducing false 503s
• Client pool 60% → 75% of burst (6 → 9 concurrent fetches): more tiles queue server-side instead of waiting client-side
• BudgetRetryAfterSeconds 5 → 6: aligned with new burst refill time (12/2=6s)
• Part D (pre-warming adjacent zoom levels) deferred with TODO — requires priority-aware token bucket

Net effect: ~19 tiles served per wave on cold-cache zoom 17 (up from ~16). OSM compliance unchanged (sustained rate 2/sec, MaxConnectionsPerServer=2).

Closes #214

Test plan

• All 1407 tests pass (dotnet test)
• Cold-cache map load: verify up to 9 concurrent tile fetches in Network tab
• Verify 503 responses include Retry-After: 6
• Verify window.wayfarerTileConfig shows burstCapacity: 12, retryAfterSeconds: 6
• Verify slow retry polls at ~18s intervals
• Multi-user cold-cache test: confirm 503+retry handles contention gracefully

[stef-k]

Code review

Found 1 issue:

1. Stale comment: line 82 still says "Falls back to 5s if config unavailable" but the fallback on line 83 was changed to 6. CLAUDE.md says "All code new and old must be documented so everytime you edit code and does not contain documentation you will have to add it."

Wayfarer/wwwroot/js/retryTileLayer.js

Lines 81 to 84 in 7e34bb5

	// replenishment cycle). Slow retry uses 3x that interval to give the per-IP sliding window
	// time to decay between attempts. Falls back to 5s if config unavailable.
	const _retryAfterSeconds = _config.retryAfterSeconds || 6;
	const _defaultSlowRetryDelayMs = _retryAfterSeconds * 3 * 1000;

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