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.

web/templates/pages/prompt_diff.html

@@ -0,0 +1,5 @@
+{{define "content"}}
+<div class="pagehead"><p class="muted small"><a href="/prompts/{{.Data.Name}}">{{.Data.Name}}</a> › diff</p><h1>v{{.Data.A.Version}} → v{{.Data.B.Version}}</h1></div>
+<div class="card"><h2>Lines</h2><pre class="json diff">{{range .Data.Lines}}<span class="{{.Class}}">{{.Text}}</span>
+{{end}}</pre></div>
+{{end}}