Add TFR warning banner for airspace restrictions

Fetches active Temporary Flight Restrictions from the FAA website,
filters by configured state (LOCATION_STATE env var), and displays
a red warning banner at the top of the dashboard when TFRs are present.
Data is cached for 30 minutes and degrades gracefully if the FAA is unreachable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/client/faa.go

@@ -0,0 +1,136 @@
+package client
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/scottyah/paragliding/internal/model"
+)
+
+const (
+	faaTFRListURL = "https://tfr.faa.gov/tfr2/list.jsp"
+	faaBaseURL    = "https://tfr.faa.gov"
+)
+
+// FAAClient fetches TFR data from the FAA website
+type FAAClient struct {
+	httpClient *http.Client
+}
+
+// NewFAAClient creates a new FAA TFR client
+func NewFAAClient() *FAAClient {
+	return &FAAClient{
+		httpClient: &http.Client{
+			Timeout: 15 * time.Second,
+		},
+	}
+}
+
+var (
+	anchorRe  = regexp.MustCompile(`(?is)<a\s+([^>]*)>(.*?)</a>`)
+	hrefRe    = regexp.MustCompile(`(?i)href="([^"]*)"`)
+	dateRe    = regexp.MustCompile(`^\d{2}/\d{2}/\d{4}$`)
+	htmlTagRe = regexp.MustCompile(`<[^>]*>`)
+)
+
+type anchor struct {
+	href string
+	text string
+}
+
+// FetchTFRs retrieves the list of active TFRs from the FAA website
+func (c *FAAClient) FetchTFRs(ctx context.Context) ([]model.TFR, error) {
+	req, err := http.NewRequestWithContext(ctx, "GET", faaTFRListURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("create request: %w", err)
+	}
+	req.Header.Set("User-Agent", "ParaglidingWeatherApp/1.0")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("fetch TFR list: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("TFR list returned status %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read response: %w", err)
+	}
+
+	return parseTFRList(string(body)), nil
+}
+
+// extractAnchors finds all <a> tags in HTML and returns their href and text content
+func extractAnchors(html string) []anchor {
+	matches := anchorRe.FindAllStringSubmatch(html, -1)
+	anchors := make([]anchor, 0, len(matches))
+	for _, m := range matches {
+		text := htmlTagRe.ReplaceAllString(m[2], "")
+		text = strings.TrimSpace(text)
+		a := anchor{text: text}
+		if hrefMatch := hrefRe.FindStringSubmatch(m[1]); hrefMatch != nil {
+			a.href = hrefMatch[1]
+		}
+		anchors = append(anchors, a)
+	}
+	return anchors
+}
+
+// parseTFRList extracts TFR entries from the FAA list page HTML.
+// The page contains a table where each row has anchor tags for:
+// date, notam ID (with detail link), facility, state, type, description, zoom link
+func parseTFRList(html string) []model.TFR {
+	rows := strings.Split(html, "<tr")
+	var tfrs []model.TFR
+
+	for _, row := range rows {
+		anchors := extractAnchors(row)
+		if len(anchors) < 6 {
+			continue
+		}
+
+		// First anchor should contain a date (mm/dd/yyyy)
+		if !dateRe.MatchString(anchors[0].text) {
+			continue
+		}
+
+		// Build detail URL from the NOTAM anchor's href
+		detailURL := anchors[1].href
+		if detailURL != "" {
+			detailURL = strings.Replace(detailURL, "..", faaBaseURL, 1)
+			detailURL = strings.ReplaceAll(detailURL, "\n", "")
+			detailURL = strings.ReplaceAll(detailURL, "\r", "")
+		}
+
+		desc := anchors[5].text
+		desc = strings.ReplaceAll(desc, "\n", "")
+		desc = strings.ReplaceAll(desc, "\r", "")
+		// Collapse multiple spaces
+		for strings.Contains(desc, "  ") {
+			desc = strings.ReplaceAll(desc, "  ", " ")
+		}
+
+		tfr := model.TFR{
+			Date:        anchors[0].text,
+			NotamID:     anchors[1].text,
+			Facility:    anchors[2].text,
+			State:       anchors[3].text,
+			Type:        anchors[4].text,
+			Description: strings.TrimSpace(desc),
+			DetailURL:   detailURL,
+		}
+
+		tfrs = append(tfrs, tfr)
+	}
+
+	return tfrs
+}