feat(dream): configurable dream.cycle_timeout (hot)

[W4-NERF]

Summary

Make the whole dream cycle timeout configurable via a hot setting (dream.cycle_timeout), mirroring dream.temporal_timeout (PR #23). Today the cycle runs under a hardcoded CycleTimeout const (700s); this PR makes it a live, restart-free knob.

Why it matters

The entire dream cycle — pick → temporal → keywords → RRF → eval → recurrence → quality-score → cooldown — runs under a single context.WithTimeout(ctx, CycleTimeout). On slow reasoning models this const is too tight:

• Qwen3.8-27B-NVFP4 runs the eval call alone for ~600–690s on full 16–20-candidate prompts.
• At a 700s cycle cap, the eval fills the budget, so the remaining steps time out inside the cycle — the cascade recurrence phase 2 failed → update quality score failed → (no cooldown set → block re-picks every cycle).
• The symptom is "Dream seems stuck / nothing promotes" while /health is green.

The only current fix is a source rebuild (const 700 → 2400). This PR makes it a hot setting, so an operator can raise the cycle deadline without a rebuild.

What changed

File	Change
internal/config/config.go	new DreamConfig.CycleTimeout — dream.cycle_timeout / CTX_DREAM_CYCLE_TIMEOUT, default 700 (legacy const), mut:hot, tenancy:global-only
internal/dream/router.go	new Router.CycleTimeout field
internal/dream/dream.go	new CycleTimeoutFor(r) helper (router value > 0 wins, else the package CycleTimeout const) + RunDreamCycle reads it
internal/events/scheduler.go	newRouter wires CycleTimeout; the outer cycle context reads the effective value
internal/config/validate.go	V16b budget reads the effective (hot) cycle deadline (temporalTimeoutBudgetOf), so a raised cycle widens the window instead of warning spuriously
internal/dream/cycle_timeout_test.go	TestCycleTimeoutFor (nil / empty / override / negative → default)
internal/config/validate_test.go	TestValidateTemporalTimeoutBudget updated (default 400s; 2400s cycle → 2100s)
docs/operations.md	new env-table row + temporal_timeout budget clause updated

Precedence: the key is the default for the enclosing cycle. A timeouts.dream entry on the serving context_backends row still wins per call (TimeoutFor, walked in llm/chain.go) — it bounds eval/keywords/recurrence per call, whereas this key bounds the whole cycle. On a configured row, raise the row value instead.

Backward compatibility

• Default 700 = the legacy CycleTimeout constant — no behavior change for existing deployments.
• 0 (and a negative value, rejected at boot / 422s the settings write by V16) falls back to the constant — same contract as temporal_timeout.
• No migrations, no schema change.

Tests & verification

• go build ./... — clean
• go vet ./internal/{dream,config,events}/ — clean
• go test -short ./internal/{dream,config,events}/ — all pass (incl. the two new/updated tests)
• golangci-lint v2 (repo config) on the 3 touched packages — 0 issues

Base: root.