feat: implement profile summary cards with GraphQL fetch and Action wrapper

- Add GraphQL client fetching profile, stats, language aggregation, and
  per-repo commit histograms for the productive-time heatmap.
- Render real SVG cards (profile details, top languages, stats grid,
  weekday×hour heatmap) with XML escaping and thousands-formatted numbers.
- Expand theme palette to 30 built-ins ported from github-readme-stats;
  add -list-themes, multi-theme rendering, and 'all' shortcut.
- Package as Docker-based GitHub Action (action.yml, Dockerfile,
  entrypoint.sh) with optional auto-commit of generated cards.
- Release workflow publishes GHCR image and cross-platform binaries on
  v* tags.
- Unit tests cover rendering, XML escape, number formatting, language sort.

internal/github/profile.go

@@ -0,0 +1,140 @@
+package github
+
+import (
+	"errors"
+	"sort"
+	"time"
+)
+
+// profileGQL mirrors the GraphQL response for profileQuery.
+type profileGQL struct {
+	User *struct {
+		ID        string `json:"id"`
+		Login     string `json:"login"`
+		Name      string `json:"name"`
+		Bio       string `json:"bio"`
+		AvatarURL string `json:"avatarUrl"`
+		Company   string `json:"company"`
+		Location  string `json:"location"`
+		Website   string `json:"websiteUrl"`
+		CreatedAt string `json:"createdAt"`
+
+		Followers struct{ TotalCount int } `json:"followers"`
+		Following struct{ TotalCount int } `json:"following"`
+
+		PullRequests struct{ TotalCount int } `json:"pullRequests"`
+		Issues       struct{ TotalCount int } `json:"issues"`
+
+		RepositoriesContributedTo struct{ TotalCount int } `json:"repositoriesContributedTo"`
+
+		ContributionsCollection struct {
+			TotalCommitContributions            int `json:"totalCommitContributions"`
+			TotalIssueContributions             int `json:"totalIssueContributions"`
+			TotalPullRequestContributions       int `json:"totalPullRequestContributions"`
+			TotalPullRequestReviewContributions int `json:"totalPullRequestReviewContributions"`
+			TotalRepositoryContributions        int `json:"totalRepositoryContributions"`
+			RestrictedContributionsCount        int `json:"restrictedContributionsCount"`
+			ContributionCalendar                struct {
+				TotalContributions int `json:"totalContributions"`
+			} `json:"contributionCalendar"`
+		} `json:"contributionsCollection"`
+
+		Repositories struct {
+			TotalCount int `json:"totalCount"`
+			PageInfo   struct {
+				HasNextPage bool   `json:"hasNextPage"`
+				EndCursor   string `json:"endCursor"`
+			} `json:"pageInfo"`
+			Nodes []repoNode `json:"nodes"`
+		} `json:"repositories"`
+	} `json:"user"`
+}
+
+// FetchProfile collects profile, stats and language data for the given user.
+// Repositories are paginated up to 10 pages (1000 owned repos) as a safety cap.
+func (c *Client) FetchProfile(login string) (*Profile, error) {
+	if login == "" {
+		return nil, errors.New("empty user")
+	}
+
+	p := &Profile{Login: login}
+	langBytes := map[string]int64{}
+	langColor := map[string]string{}
+
+	var cursor *string
+	const maxPages = 10
+	for page := 0; page < maxPages; page++ {
+		vars := map[string]any{"login": login}
+		if cursor != nil {
+			vars["after"] = *cursor
+		}
+
+		var resp profileGQL
+		if err := c.query(profileQuery, vars, &resp); err != nil {
+			return nil, err
+		}
+		if resp.User == nil {
+			return nil, errors.New("user not found")
+		}
+		u := resp.User
+
+		if page == 0 {
+			p.ID = u.ID
+			p.Name = u.Name
+			p.Bio = u.Bio
+			p.AvatarURL = u.AvatarURL
+			p.Company = u.Company
+			p.Location = u.Location
+			p.Website = u.Website
+			if t, err := time.Parse(time.RFC3339, u.CreatedAt); err == nil {
+				p.CreatedAt = t
+			}
+			p.Followers = u.Followers.TotalCount
+			p.Following = u.Following.TotalCount
+			p.PublicRepos = u.Repositories.TotalCount
+			p.TotalPRs = u.PullRequests.TotalCount
+			p.TotalIssues = u.Issues.TotalCount
+			p.TotalContributedTo = u.RepositoriesContributedTo.TotalCount
+
+			cc := u.ContributionsCollection
+			p.TotalCommits = cc.TotalCommitContributions
+			p.TotalReviews = cc.TotalPullRequestReviewContributions
+			p.TotalContributions = cc.ContributionCalendar.TotalContributions + cc.RestrictedContributionsCount
+		}
+
+		for _, r := range u.Repositories.Nodes {
+			p.TotalStars += r.StargazerCount
+			p.TotalForks += r.ForkCount
+			p.TopRepos = append(p.TopRepos, r.Name)
+			for _, e := range r.Languages.Edges {
+				langBytes[e.Node.Name] += e.Size
+				if _, ok := langColor[e.Node.Name]; !ok {
+					langColor[e.Node.Name] = e.Node.Color
+				}
+			}
+		}
+
+		if !u.Repositories.PageInfo.HasNextPage {
+			break
+		}
+		end := u.Repositories.PageInfo.EndCursor
+		cursor = &end
+	}
+
+	p.Languages = sortLanguages(langBytes, langColor)
+	return p, nil
+}
+
+func sortLanguages(bytes map[string]int64, color map[string]string) []LangStat {
+	out := make([]LangStat, 0, len(bytes))
+	for name, b := range bytes {
+		out = append(out, LangStat{Name: name, Color: color[name], Bytes: b})
+	}
+	sort.Slice(out, func(i, j int) bool {
+		if out[i].Bytes != out[j].Bytes {
+			return out[i].Bytes > out[j].Bytes
+		}
+		return out[i].Name < out[j].Name
+	})
+	return out
+}