feat(gitea): IssueTracker client + inject into brain server (#52)

Implements the IssueTracker port as a real Gitea REST client (#49c) — the
new outbound dependency the brain server gains for capture.

- CreateIssue / CommentIssue / CloseIssue(+optional closing comment) over
  the Gitea API. Owner is the const "mathias", never caller-supplied, so
  a caller cannot redirect a write to another owner's repo.
- Token read once at construction (BRAIN_GITEA_TOKEN), held in the struct,
  travels only in the Authorization header — never logged or in argv.
  Error messages carry status + truncated body, never the token
  (regression-tested). gitea.New returns nil when URL or token is unset,
  so missing config = tracker disabled via one nil check.
- Injected into the MCP server behind the capture.IssueTracker interface
  via WithIssueTracker (constructor injection, swappable/testable); main
  wires it from BRAIN_GITEA_URL (default https://git.d-ma.be) +
  BRAIN_GITEA_TOKEN. Consumed by the capture use-case in #53.

Tests use httptest transports: create (owner+auth header asserted),
comment, close with/without comment, error path that proves the token
never leaks into an error string.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ingestion/internal/gitea/gitea.go

@@ -0,0 +1,129 @@
+// Package gitea implements capture.IssueTracker against a Gitea instance
+// over its REST API. It is the new outbound dependency the brain server
+// gains for the capture capability (#49c/#52): the server otherwise does
+// brain-local file ops only.
+//
+// Owner is hard-coded to the operator and never taken from caller input.
+// The API token is read once at construction, held in the struct, and
+// never logged or placed in argv — it travels only in the Authorization
+// header of outbound requests (AGENTS.md secret-handling).
+package gitea
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/capture"
+)
+
+// owner is the fixed repository owner for every ticket operation. It is a
+// constant, not a parameter, so a caller can never redirect a write to
+// another owner's repo.
+const owner = "mathias"
+
+// Client is a Gitea REST API IssueTracker.
+type Client struct {
+	baseURL string
+	token   string
+	http    *http.Client
+}
+
+// New constructs a Client. It returns nil when either baseURL or token is
+// empty, so callers can treat missing config as "tracker disabled" with a
+// single nil check (mirrors embed.New).
+func New(baseURL, token string) *Client {
+	if baseURL == "" || token == "" {
+		return nil
+	}
+	return &Client{
+		baseURL: strings.TrimRight(baseURL, "/"),
+		token:   token,
+		http:    &http.Client{Timeout: 15 * time.Second},
+	}
+}
+
+// issueResponse is the subset of a Gitea issue/comment payload we read.
+type issueResponse struct {
+	Number  int    `json:"number"`
+	HTMLURL string `json:"html_url"`
+}
+
+// CreateIssue opens a new issue under the fixed owner.
+func (c *Client) CreateIssue(ctx context.Context, repo, title, body string) (capture.IssueRef, error) {
+	var out issueResponse
+	if err := c.do(ctx, http.MethodPost,
+		fmt.Sprintf("/api/v1/repos/%s/%s/issues", owner, repo),
+		map[string]any{"title": title, "body": body}, &out); err != nil {
+		return capture.IssueRef{}, err
+	}
+	return capture.IssueRef{Repo: repo, Number: out.Number, URL: out.HTMLURL}, nil
+}
+
+// CommentIssue posts a comment on an existing issue.
+func (c *Client) CommentIssue(ctx context.Context, repo string, number int, body string) (capture.IssueRef, error) {
+	var out issueResponse
+	if err := c.do(ctx, http.MethodPost,
+		fmt.Sprintf("/api/v1/repos/%s/%s/issues/%d/comments", owner, repo, number),
+		map[string]any{"body": body}, &out); err != nil {
+		return capture.IssueRef{}, err
+	}
+	return capture.IssueRef{Repo: repo, Number: number, URL: out.HTMLURL}, nil
+}
+
+// CloseIssue closes an issue, first posting a closing comment when one is
+// given (empty comment ⇒ close only).
+func (c *Client) CloseIssue(ctx context.Context, repo string, number int, comment string) (capture.IssueRef, error) {
+	if strings.TrimSpace(comment) != "" {
+		if _, err := c.CommentIssue(ctx, repo, number, comment); err != nil {
+			return capture.IssueRef{}, err
+		}
+	}
+	var out issueResponse
+	if err := c.do(ctx, http.MethodPatch,
+		fmt.Sprintf("/api/v1/repos/%s/%s/issues/%d", owner, repo, number),
+		map[string]any{"state": "closed"}, &out); err != nil {
+		return capture.IssueRef{}, err
+	}
+	return capture.IssueRef{Repo: repo, Number: number, URL: out.HTMLURL}, nil
+}
+
+// do performs a JSON request against the Gitea API and decodes the
+// response into out. Errors carry the status and a truncated body for
+// diagnosis but never the token.
+func (c *Client) do(ctx context.Context, method, path string, payload any, out *issueResponse) error {
+	reqBody, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal request: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, c.baseURL+path, bytes.NewReader(reqBody))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	// Gitea's token scheme. Held here only; never logged.
+	req.Header.Set("Authorization", "token "+c.token)
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return fmt.Errorf("gitea %s %s: %w", method, path, err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("gitea %s %s: status %d: %s", method, path, resp.StatusCode, strings.TrimSpace(string(respBody)))
+	}
+	if out != nil && len(respBody) > 0 {
+		if err := json.Unmarshal(respBody, out); err != nil {
+			return fmt.Errorf("gitea %s %s: decode response: %w", method, path, err)
+		}
+	}
+	return nil
+}