feat: add long-term memory systems with fused retrieval and memory explorer

Phase 5 (ADR-0003). pkg/concepts fixes the epistemic vocabulary
(observation, fact, memory, claim, hypothesis, belief, prediction,
assumption, inference, opinion), memory kinds and relation names.

internal/memory stores episodic, semantic, procedural and
autobiographical memories in one mind-scoped table with trust-derived
credibility, importance, salience and decaying activation. Retrieval
fuses full-text rank (any-term by default), optional pgvector similarity,
recency, activation, importance and credibility, and returns the
component scores so every recall can be explained. Decay lowers
activation and never deletes; retraction and supersession keep rows for
provenance. Relationships are constrained to one mind at insert time.
Embeddings live in a conditional pgvector table keyed by model so vector
spaces are never mixed; without an embedder the system degrades to text
and graph retrieval.

Attention gates encoding: the attend handler turns admitted observations
into episodic memories (operator changes become autobiographical ones)
with memory_created events; the retrieve process proposes recalled
memories as candidates and admitted recalls are reinforced with
memory_retrieved events carrying their scoring components.

Memory explorer UI (search with component breakdown, timeline, filters,
operator knowledge entry), memory detail with provenance, relationships,
citing events and an inaccurate-memory correction; API; noemactl memory
commands; decay and embed-missing background jobs.

pkg/concepts/concepts.go

@@ -0,0 +1,89 @@
+// Package concepts defines the epistemic vocabulary Noema refuses to collapse:
+// the difference between an observation, a claim, a hypothesis and a belief is
+// carried on every memory, belief and evidence link (spec §0.1).
+package concepts
+
+// Epistemic classifies how something is known.
+type Epistemic string
+
+// Epistemic kinds.
+const (
+	Observation Epistemic = "observation" // directly perceived through a channel
+	Fact        Epistemic = "fact"        // verified against an authoritative source
+	Memory      Epistemic = "memory"      // recalled episode; subject to distortion
+	Claim       Epistemic = "claim"       // asserted by someone else, unverified
+	Hypothesis  Epistemic = "hypothesis"  // proposed explanation under evaluation
+	Belief      Epistemic = "belief"      // held with confidence derived from evidence
+	Prediction  Epistemic = "prediction"  // expectation about the future
+	Assumption  Epistemic = "assumption"  // taken as given without evidence
+	Inference   Epistemic = "inference"   // derived by reasoning from other items
+	Opinion     Epistemic = "opinion"     // preference or judgement, not truth-apt
+)
+
+// AllEpistemic lists kinds in a stable order.
+var AllEpistemic = []Epistemic{Observation, Fact, Memory, Claim, Hypothesis, Belief, Prediction, Assumption, Inference, Opinion}
+
+// Valid reports whether e is known.
+func (e Epistemic) Valid() bool {
+	for _, k := range AllEpistemic {
+		if k == e {
+			return true
+		}
+	}
+	return false
+}
+
+// MemoryKind is the storage system a memory belongs to.
+type MemoryKind string
+
+// Memory kinds (spec §8).
+const (
+	Episodic         MemoryKind = "episodic"
+	Semantic         MemoryKind = "semantic"
+	Procedural       MemoryKind = "procedural"
+	Autobiographical MemoryKind = "autobiographical"
+)
+
+// AllMemoryKinds lists kinds in a stable order.
+var AllMemoryKinds = []MemoryKind{Episodic, Semantic, Procedural, Autobiographical}
+
+// Valid reports whether k is known.
+func (k MemoryKind) Valid() bool {
+	for _, x := range AllMemoryKinds {
+		if x == k {
+			return true
+		}
+	}
+	return false
+}
+
+// Relation labels an edge between memories or entities.
+type Relation string
+
+// Relations (spec §24).
+const (
+	RelatedTo      Relation = "related_to"
+	CausedBy       Relation = "caused_by"
+	Contradicts    Relation = "contradicts"
+	Supports       Relation = "supports"
+	DependsOn      Relation = "depends_on"
+	BelongsTo      Relation = "belongs_to"
+	DiscussedWith  Relation = "discussed_with"
+	ObservedDuring Relation = "observed_during"
+	DerivedFrom    Relation = "derived_from"
+	SimilarTo      Relation = "similar_to"
+	Follows        Relation = "follows"
+)
+
+// AllRelations lists relations in a stable order.
+var AllRelations = []Relation{RelatedTo, CausedBy, Contradicts, Supports, DependsOn, BelongsTo, DiscussedWith, ObservedDuring, DerivedFrom, SimilarTo, Follows}
+
+// Valid reports whether r is known.
+func (r Relation) Valid() bool {
+	for _, x := range AllRelations {
+		if x == r {
+			return true
+		}
+	}
+	return false
+}