providers: coerce numeric config knobs to numbers at send time

[jeffdafoe]

Symptom

salem-visitor (anthropic / claude-haiku-4-5) chat fails on every dispatch:

```
Anthropic API error 400: {"type":"error","error":{"type":"invalid_request_error",
"message":"temperature: Input should be a valid number"}}
```

Engine logs the failure, visitor never decides anything, sits forever outside the tavern.

Cause

The admin Settings panel (agents.js:449) round-trips numeric knobs through `agentSettingsConfig.value`, which inherits the string-typed values `pg` returns for `numeric` columns. The save persists them into `agent_configuration.configuration` as strings (e.g. `{"temperature":"0.7"}`), then each provider passes them straight through to the upstream API.

OpenRouter / Llama happen to coerce strings on their end, so the bug stayed latent there. Anthropic does not — it rejects with HTTP 400. OpenAI, Google, Perplexity, xAI would all fail the same way for any agent saved through the Settings panel; it just hadn't been exercised yet.

Fix

New `providers/coerce.js` exports `asNumber(v)`: returns a finite number for valid inputs, `undefined` for null / empty / NaN / Infinity / non-numeric strings.

Lives in its own module rather than `providers/index.js` to avoid the circular require chain (index.js loads each provider by name; providers can't require index.js back).

Each provider calls `asNumber` on numeric body fields before assigning. Storage stays whatever the user typed (no migration needed); each provider enforces its own type contract at send time.

Coverage:

• anthropic.js: temperature, max_tokens
• openai.js: temperature, max_tokens, max_completion_tokens (both /v1/responses and chat/completions paths)
• google.js: temperature, max_tokens, top_p, top_k, thinking_budget
• openrouter.js: temperature, max_tokens
• perplexity.js: temperature, max_tokens
• xai.js: temperature, max_output_tokens

Blast radius

• Strings now become numbers before reaching the provider API. No call sites outside the providers — coerce.js is provider-internal.
• Bad input (non-numeric string, NaN, Infinity) is silently dropped instead of being passed through. Provider falls back to its own default. Acceptable: matches the existing behavior for empty-string + sanitizeAgentConfiguration in the admin save path, just extended to the runtime contract.
• No change for already-numeric values — `asNumber(0.7)` returns `0.7` unchanged.

Test plan

• Local smoke test: `require('./src/services/providers')` loads cleanly (no circular dep).
• `asNumber` matrix: '0.7' → 0.7, 0.7 → 0.7, '' → undefined, null → undefined, undefined → undefined, 'abc' → undefined, '0' → 0, 'Infinity' → undefined.
• Deploy. Verify next salem-visitor tick (Caleb or Elias, both currently parked outside the tavern) actually reaches Anthropic and produces a tool call or speech.
• Spot-check an OpenAI agent — should still work (was already passing numbers, this is a no-op for numeric input).
• Spot-check Hannah Boggs (salem-vendor / openrouter) — should still work; openrouter happens to coerce on its end but now we coerce locally too.

— Home