feat: add conversation with grounded replies, sample mind and M1 acceptance test

Phase 8, completing milestone M1. A user message is stored and appended
as an observation event carrying trust, actor, channel and reference. The
perceive process analyses it deterministically (intent, introspection
kind, entities, claims, urgency) and, within the per-cycle model
allowance, enriches it through the perceive prompt. Its handler writes a
perception event, an episodic memory with participants, turns claims into
beliefs whose evidence is the message, and builds a response intent from
state: beliefs and memories for the topic, evidence rows for why-questions,
the uncertain band, contested beliefs and their links, recent learning,
status changes, and honest declines for subsystems that do not exist yet
or for requests with no capabilities. The respond prompt phrases the
intent when a model is assigned; otherwise the reply is a direct
rendering of the intent. response_generated cites the message, the
perception, every belief and memory used, the episode and the model call.

API: conversations, messages with optional wait, one-shot ask; chat UI
with live refresh and a per-reply intent view. Sample mind Dani as a
strictly decoded seed document with an import endpoint and noemactl mind
import. tests/m1 drives all fourteen milestone steps including restart.

CHANGELOG.md

@@ -5,6 +5,7 @@ All notable changes to Noema are recorded here. Format follows Keep a Changelog;
 ## [Unreleased]
 
 ### Added
+- Phase 8 conversation (milestone M1): messages become observations, deterministic perception with optional model enrichment, claims become evidenced beliefs, grounded introspective answers from real state, model or deterministic wording with full provenance, chat UI, `noemactl ask`, sample mind Dani with a strict seed import, and an end-to-end acceptance test.
 - Phase 7 LLM layer: provider-neutral router with roles and fallbacks, OpenAI-compatible/Anthropic/Ollama providers, encrypted secret references, SSRF-safe HTTP client, budgets, full call recording with replay, versioned prompts with untrusted data blocks, configuration and prompt manager UI, CLI.
 - Phase 6 beliefs: evidence-derived confidence with inspectable arithmetic, statuses, alternatives, append-only history, deterministic contradiction detection, temporal-association hypotheses, operator corrections (wrong, do-not-infer, inaccurate memory), belief explorer and CLI.
 - Phase 5 memory: episodic/semantic/procedural/autobiographical memory with epistemic status, fused retrieval with inspectable component scores, optional pgvector embeddings, decay without deletion, attention-gated encoding, retrieval process, memory explorer and CLI.