Phase 7: daily summary and read-only Hub API (AUD-73)

- internal/hub: project side of the frozen ask-contract. GET /capabilities,
  read-only POST /ask answerer (no LLM, <3s), and the outbound POST /notify
  client.
- internal/apprise: daily-summary delivery through the house Apprise API.
- internal/summary: deterministic plain-text daily summary builder.
- internal/store: CountByCategory, MessagesByCategory, and summary CRUD.
- internal/server: /capabilities and /ask (bearer-token protected), plus the
  Reports screen (/reports, build, send, delete).
- main.go: -summary, -summary-send, and -notify CLI entry points for n8n.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/hub/hub.go

@@ -0,0 +1,93 @@
+// Package hub implements the project side of the Hub contract
+// (central_ai_llm_master/docs/ask-contract.md) and the outbound notify call.
+//
+// The contract is one-directional by design: the Hub asks a project about its
+// own data and the project answers. A project never learns the Hub's data model
+// and the Hub never learns the project's. The project endpoints are
+// GET /capabilities and POST /ask (read only); POST /notify is the
+// project-to-Hub direction.
+//
+// Phase 7 (FR-12). Answers are computed from SQLite; /ask performs no writes.
+package hub
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/store"
+)
+
+// ProjectName is the value the Hub matches in routing.md.
+const ProjectName = "email_agent"
+
+// Capabilities is the GET /capabilities reply. The Hub reads it to route a
+// question to this project. Keep the topic list short and plain; it holds no
+// private data.
+type Capabilities struct {
+	Project string   `json:"project"`
+	Topics  []string `json:"topics"`
+	People  []string `json:"people"`
+}
+
+// DefaultCapabilities returns the topics this service can answer. "email",
+// "inbox", "mail", and "message" match the routing.md topic map. Read/unread is
+// deliberately absent: the service does not track read state.
+func DefaultCapabilities() Capabilities {
+	return Capabilities{
+		Project: ProjectName,
+		Topics:  []string{"email", "inbox", "mail", "message"},
+		People:  []string{"sam"},
+	}
+}
+
+// AskRequest is the POST /ask body (ask-contract.md).
+type AskRequest struct {
+	Question string `json:"question"`
+	Asker    string `json:"asker"`
+	Person   string `json:"person,omitempty"`
+	Source   string `json:"source,omitempty"`
+}
+
+// AskResponse is the POST /ask reply. A nil Answer means the project cannot
+// answer and Reason explains why. The shape is frozen by the contract.
+type AskResponse struct {
+	Answer  *string        `json:"answer"`
+	Data    map[string]any `json:"data,omitempty"`
+	Expires string         `json:"expires,omitempty"`
+	Reason  string         `json:"reason,omitempty"`
+}
+
+// answerText is a small helper so the pointer handling stays in one place.
+func answerText(s string) *string { return &s }
+
+// cannotAnswer builds the contract's "cannot answer" reply.
+func cannotAnswer(reason string) AskResponse {
+	return AskResponse{Answer: nil, Reason: reason}
+}
+
+// expiresIn formats an RFC3339 expiry used by data-bearing answers. An inbox
+// answer goes stale quickly because mail arrives and is triaged.
+func expiresIn(now time.Time, d time.Duration) string {
+	return now.UTC().Add(d).Format(time.RFC3339)
+}
+
+// NotifyRequest is the project-to-Hub POST /notify body (ask-contract.md). The
+// Hub may use it to speak or notify.
+type NotifyRequest struct {
+	From    string `json:"from"`
+	Level   string `json:"level"`
+	Message string `json:"message"`
+	Person  string `json:"person,omitempty"`
+}
+
+// jsonBody marshals a notify payload, kept small and deterministic for tests.
+func jsonBody(v any) ([]byte, error) { return json.Marshal(v) }
+
+// Reader is the read-only data surface the answerer uses. *store.Store
+// satisfies it; tests can supply a fake. Keeping it an interface makes the
+// read-only guarantee explicit and easy to assert.
+type Reader interface {
+	CountByCategory(ctx context.Context, folder string) ([]store.CategoryCount, error)
+	MessagesByCategory(ctx context.Context, folder string, categories []string, limit int) ([]store.MessageListItem, error)
+}