feat: add provider-neutral LLM layer with secrets, budgets, recording and prompts

Phase 7 (ADR-0004). Cognitive code asks the router for a role; the
router maps roles to configured models with ordered fallbacks, applies
global and per-mind daily token budgets and a concurrency limit, records
every call (request, response, usage, latency, cost, seed, request hash)
and can serve recordings back for exact replay. Providers are raw HTTP
clients for OpenAI-compatible, Anthropic and Ollama endpoints, with
embedding support for the embed role wired into memory retrieval.

Secrets are references only: env:, file:, or enc: values encrypted with
AES-256-GCM under NOEMA_MASTER_KEY; keys are resolved at call time and
never rendered, logged or exported. Outbound HTTP refuses private and
loopback addresses at dial time unless a provider explicitly allows it,
bounds redirects and caps bodies. Provider errors are scrubbed.

Prompts are named, versioned rows with system and user templates and an
optional JSON schema; untrusted text enters only through delimited data
blocks. Six defaults are seeded and never overwritten. The UI adds the
LLM page (providers, models, role matrix, usage, errors, budgets), a
provider page with connectivity test, and a prompt manager with editor,
test runner, history, restore, clone and diff. CLI: provider, prompt.

internal/llm/prompts/defaults/hypothesise.tmpl

@@ -0,0 +1,15 @@
+---
+role: hypothesise
+description: Propose candidate explanations for a set of observations.
+schema: {"type":"object","properties":{"hypotheses":{"type":"array","items":{"type":"object","properties":{"proposition":{"type":"string"},"mechanism":{"type":"string"},"evidence_needed":{"type":"array","items":{"type":"string"}},"prior_plausibility":{"type":"string","enum":["low","medium","high"]}}}}},"required":["hypotheses"]}
+system: |
+  You generate candidate explanations. You do not decide what is true; another component weighs evidence.
+  Prefer mundane explanations. Always include at least one alternative that the observations are unrelated. Output JSON only.
+---
+Observations (most recent last):
+{{range .Observations}}{{data "observation" .}}
+{{end}}
+Existing beliefs that may be relevant:
+{{range .Beliefs}}- {{.Proposition}} ({{printf "%.2f" .Confidence}})
+{{end}}
+Propose up to {{.Max}} hypotheses. For each give the proposition, a mechanism, what evidence would raise or lower it, and a rough prior plausibility.